ANSWER

EXPLANATION
The given expression is

This is the same as:

In index notation, we write this as

To write this as a negative index, we use the property:

This implies that;

Bundle (31 , 40) has 40 bananas.
So 40 - 28 = 12 bananas
These 12 banana give the consumer negative utility which will be balance one for one apple.
So we have to need 12 apple to balance it.
So the final utility of apples and banana is 28 + (31 - 12) = 28 + 19 = 43
In second bundle (X , 23) has 23 bananas. We need to get the same utility 43.
Which we will get from 43 - 23 = 20 apples.
So X equal to 23.
The first stone will be 10-in wide
The last stone will be 10-in wide
The stones in the middle will be alternating between 5-in and 10-in stones, making a total of 15-in
Total width = 145-in
Width after placing first and last stones = 145 - 20 = 125-in
Number of 15-in patterns incorporated in 125-in:
125/15 = 8.33
Therefore, he will place 8 10-inch stones within and 9 5-inch stones within the patter.
The total 10-inch stones used = 8 + 2 = 10
They would cost 2 pounds.