Question

Liza hired a cleaning service to clean her house. To find C, the total cost of cleaning her house, she used the following formula: C = 0.5x - 3

Answer 1

I think the formula is a typo.
Perhaps C= 0.5 x + 3
???
C = 2 + 3 = 5
and by the way 0.5 * 4 = 2 not 1.5

Answer 2

C = 0.5x - 3

where x is the number of hours the cleaning service worked.

If the cleaning service worked for 4 hours, what is the total cost of cleaning Liza's house?

C = 0.5(4) - 3
C = 1.5 - 3
C = -1.5