A manufacturer of widgets finds that the production cost, C, in dollars per unit is a function of the number of widgets produced. The selling price, S, of each widget in dollars is a function of the production cost per unit. C(x)=-0.1x^2+100 S(C)=1.4C

I guess that you want to find the profit:

We have two equations:

the cost equation:

C(x) = -0.1*x^2 + 100.

And the selling equation, that is a vertical stretch of the cost equation by a factor of 1.4:

S(x) = 1.4*C(x) = 1.4*( -0.1*x^2 + 100.) = -0.14*x^2 + 140

Now, whit those two equations we can find the profit equation, that is defined as the difference between the selling price, and the cost:

P(x) = S(x) - C(x) = 1.4*C(x) - C(x) = (1.4 - 1)*C(x) = 0.4*C(x).

Then the profit is 0.4 times the initial cost.

P(x) = 0.4*( -0.1*x^2 + 100.) = -0.04*x^2 + 40

your answer would be 12