Question

Am I right. if not please show me work thx.

Answer 1

If you're talking about #3, then the equation would be 10+12.50h=5+15h.
h will equal 2, and the cost for that number of hours would then be $35.

Answer 2

Your output for C should be 15 
Your input for D should be 100

Yup Kittlesbug is right for the third one NICE!