Simple...
you have:
2.) A plumber charges $25 per hour plus an additional $99 for parts. If the plumber worked for 4 hours, which equation represents the total cost for C?
Using y=mx+b
So it's $25 per hour and $99 for parts.
C=25x+99
He worked for 4 hours--->>C=25(4)+99
3.)A gym charges $35 per month for full access to their work equipment. Miss Lewis has a $140 gift certificate to the gym.
Write an equation:
Using y=mx+b
y=-35x+140
How many months can she work out using the gift certificate?
y=-35(1)+140
y=105
y=-35(2)+140
y=70
y=-35(3)+140
y=35
y=-35(4)+140
y=0
She can use the gift certificate for 4 months...
Thus, your answer.