Final answer:
Hashim originally had $87.90.
Step-by-step explanation:
To solve this problem, we can set up an equation. Let's say Hashim had x dollars initially. After giving his mother $28, he had $15.20 less than his sister who had $75.10. This can be represented as: x - 28 = 75.10 - 15.20. Solving this equation, we can find the value of x, which is the initial amount of money Hashim had.
x - 28 = 75.10 - 15.20
x - 28 = 59.90
x = 59.90 + 28
x = 87.90
Therefore, Hashim originally had $87.90.