Let $x$ be the number of hours the freight train traveled before the diesel train caught up.
Since the diesel train left one hour later, it traveled for $x - 1$ hours when it caught up.
The distance traveled by the freight train is $28x$ miles.
The distance traveled by the diesel train is $33(x - 1)$ miles.
When the diesel train catches up, both trains have traveled the same distance:
$$
28x = 33(x - 1)
$$
Solve for $x$:
$$
28x = 33x - 33
$$
$$
28x - 33x = -33
$$
$$
-5x = -33
$$
$$
x = \frac{33}{5} = 6.6
$$
The freight train traveled for 6.6 hours before the diesel train caught up.
Parent Tip: Review the logic above to help your child master the concept of distance rate x time worksheet.