Final answer:
To make Paul just as well off as with the pizza certificate, his grandmother could give him $60 in cash, which would allow him to buy 4 pizzas and 6 hamburgers.
Step-by-step explanation:
To determine the amount of cash that Paul's grandmother could give him to make him just as well off as with the pizza certificate, we need to find the combination of pizza and hamburgers that Paul can purchase with his income. Since the price of pizza is $3 and the price of hamburgers is $6, we can set up the following equation:
3P + 6H = 240, where P is the quantity of pizza and H is the quantity of hamburgers.
Solving this equation, we find that P = (240 - 6H) / 3.
We can substitute this value of P into Paul's utility function to find his utility:
U = (240 - 6H) / 3 + 4H = (240 - 2H + 12H) / 3 = (240 + 10H) / 3
To make Paul just as well off as with the pizza certificate, we need to find the amount of cash that gives him the same utility. Setting the utility with cash equal to the utility with the pizza certificate:
(240 + 10H) / 3 = (240 + 60) / 3
240 + 10H = 240 + 60
10H = 60
H = 6
Substituting this value of H back into the equation for P, we find that:
P = (240 - 6(6)) / 3 = 12 / 3 = 4
Therefore, Paul could be just as well off with $60 in cash, which would allow him to buy 4 pizzas and 6 hamburgers.