Suppose the total utility derived from first four units of a-08931

Suppose the total utility derived from first four units of a good consumed are 12, 22, 32, and 42 respectively. What is the marginal utility of the third unit?

This multiple choice question (MCQ) is related to the book/course vu eco401 Economics. It can also be found in vu eco401 Final Term - Quiz No.18.