Given:
The price of a 2-hour plumbing repair job is $150
And the price of a 5-hour job is $330.
The general equation will have the form:
[tex]C=m\cdot t+b[/tex]Where t is the hours and C is the cost:
By the given information, we can write the following equations:
[tex]\begin{gathered} 150=2m+b\rightarrow(1) \\ 330=5m+b\rightarrow(2) \end{gathered}[/tex]Solving the equations to find the values of m and b:
Subtract (1) from (2):
[tex]\begin{gathered} 330-150=5m-2m \\ 180=3m \\ m=\frac{180}{3}=60 \end{gathered}[/tex]Substitute with (m) into equation (1) to find (b):
[tex]\begin{gathered} 150=2\cdot60+b \\ 150=120+b \\ b=150-120=30 \end{gathered}[/tex]So, the equation will be:
[tex]C=60t+30[/tex]When t = 6 hours:
[tex]C=60\cdot6+30=360+30=390[/tex]So, the answer will be option b. C = 60t + 30; 390
