Answer:

Explanation:
Given that:
Cost of book that Tyler wants to buy for his school = $13
He wants to buy books for his sisters as well.
Total amount of money present with Tyler = $27
Money to be spent on books for his sisters is same and is represented as
.
To find:
The value of
.
Solution:
As per question statement, the sum of all the books bought must be equal to $27.
The sum of money spent on all the books = Cost of Tyler's book + Cost of books for his sisters

Therefore, Tyler must spend $7 on each of her sister's books.