Math worksheet with integer problems and a riddle about a sheep with 13 hearts.

Explanation:
We are given a worksheet with two parts:

Part 1: Solve the arithmetic problems.
Each problem is either addition or subtraction of integers (positive and negative numbers). Let’s solve each one carefully.

① 4 + (−12) = 4 − 12 = −8
② −1 − (−2) = −1 + 2 = 1
③ 8 − (−5) = 8 + 5 = 13
④ −4 + 3 = −1
⑤ −3 − 8 = −11
⑥ −7 − (−7) = −7 + 7 = 0
⑦ 7 + (−4) = 7 − 4 = 3
⑧ 6 + (−10) = 6 − 10 = −4
⑨ −20 + 12 = −8
⑩ −1 − (−3) = −1 + 3 = 2
⑪ 13 − (−5) = 13 + 5 = 18
⑫ −11 − 5 = −16
⑬ 6 + (−3) = 6 − 3 = 3
⑭ −16 + 1 = −15
⑮ −3 + (−10) = −13
⑯ −7 + (−8) = −15
⑰ −8 + (−4) = −12
⑱ −8 + 5 = −3
⑲ −2 + 10 = 8

Let me double-check a few tricky ones:
- ②: subtracting a negative means adding → −1 + 2 = 1 ✔
- ⑥: −7 − (−7) = −7 + 7 = 0 ✔
- ⑪: 13 − (−5) = 13 + 5 = 18 ✔
- ⑮: −3 + (−10) = −13 ✔
All correct.

Now, Part 2: “What has 13 hearts, but no other organs?”
This is a riddle. We’re given a list of numbers under “13”, then a row of operations, then a final row of results:

Top row:
13 −16 2 −18 −3 9 1

Middle row (operations):
−15 8 −4 −17 −1 −11 3

Bottom row (results):
18 −8 −13 −12 0

Wait — actually, looking more closely, it seems the riddle is solved by matching letters to the answers from Part 1. The instruction says:
> “Then, solve the riddle by matching the letters to the blank lines below.”

But in the image, there are blank lines labeled with numbers (like ①, ②…), and likely each answer corresponds to a letter (A=1, B=2, ..., Z=26, or maybe using the result values to find letters).

However, the riddle part shows:

“What has 13 hearts, but no other organs?”
Then a table with:
- First row: 13, −16, 2, −18, −3, 9, 1
- Second row: −15, 8, −4, −17, −1, −11, 3
- Third row: 18, −8, −13, −12, 0

Wait — this looks like a cipher where you add/subtract the numbers vertically? Let's test:

Column 1: 13 + (−15) = −2 → not helpful
Or maybe: top − middle = bottom?
13 − (−15) = 28 ≠ 18
13 + (−15) = −2 ≠ 18

Alternative idea: The bottom row may be the *answers* to the arithmetic problems above, and those answers map to letters (e.g., A=1, B=2, ..., Z=26; negative numbers might wrap or use absolute value? Unlikely.)

But look again: There are 19 arithmetic problems (① to ⑲), and the riddle likely uses some of those answers to spell a word.

The riddle: “What has 13 hearts, but no other organs?”
Classic riddle answer: a deck of cards — because a standard deck has 13 hearts (the heart suit has 13 cards: Ace through King), and cards aren’t alive, so they have no organs.

Yes! That’s a well-known riddle.
“13 hearts” → the Hearts suit in a deck of playing cards has 13 cards.
“No other organs” → it’s not a living thing.

So the answer to the riddle is: a deck of cards (or simply “deck of cards”).

The arithmetic part may be for practice, but the final question is the riddle.

Since the user only asks to “solve the problem accurately”, and the main puzzle is the riddle at the bottom, the expected final answer is the solution to the riddle.

Final Answer:
a deck of cards