Short answer:
TotalCost = 12.96
Long answer:
It gives you the equation of
total cost = C + 0.08C
You just need to plug-in the $12 to the equation.
In other words, the equation is:
TotalCost = 12 + 0.08*12
TotalCost = 12 + 0.96
TotalCost = 12.96
Y2-Y1. 77-11 66 11
———— = ———- = —- = —
X2-X1 42-6 36 6
Well, we can see that the y-intercept is (0, -4) which means that the line must be:
y=mx-4
And since only one answer has -4 as the y-intercept, y=x-4 is the answer :P