Answer: a) 15 utils
Step-by-step explanation:
Let marginal utility= MU
MU of first cookie= 25 utils
MU of second cookies= 20
utils
MU of third cookies= ?
Total MU= 60 utils
MU of third cookies= Total MU- first MU- Second MU
MU of third cookies= 60 utils -
25 utils - 20 utils
MU of third cookies = 15 utils