To answer the question, you need an equation like y=A(x-h)^2+k, with (h,k) being the (x,y) coordinates of the vertex, the values of which gives the number of watches Bob must repair to have the lowest cost
C(x) = 4x2-296x+85completing the square: (factor out 4, then take half of the coefficient of the x-term and square it=(74/2)^2=37^2, then add it in to complete the square.)C(x)=4(x^2-74x+37^2)+85-4(37^2)
C(x)=4(x-37)^2+85-5476C(x)=4(x-37)^2-5391This is a parabola with vertex at (37,-5391)Ans:Bob must repair 37 watches to have the lowest operating cost See graph below ...