Solve the riddle by evaluating math expressions and matching answers to letters.
A math worksheet from SplashLearn titled "Solve the Riddle," featuring six expressions to evaluate, each associated with a letter (R, S, T, E, C). Below, a riddle asks, "If I have it, I don't share it. If I share it, I don't have it. What is it?" with answer options: 588, 2,088, 507, 99, 40, 210.