Answer:
20
Step-by-step explanation:
The computation of the marginal utility of the third slice is shown below:
= Total utility from three slices of pizza - second yield an additional units of utility - first slice of pizza units of utility
= 90 units - 28 units - 42 units
= 90 units - 70 units
= 20
The amount are mistakenly repeated in the question
Basically we deduct the first and second utility from the total utility