-9 -9 5. Find the values of a and b so that f(x) = ax + 9x + b has a local minimum at 4 8 6. Find the values of a, b and c so that f(x) = 8x + ax + bx + c has y-intercept at 5, a local minimum when x = and an inflection point when x = - 1 48. 3. Suppose the output at a certain factory is Q = 2x + xy + y units, where x is the number of hours of skilled labor used and y is the number of hours of unskilled labor. The current labor force consists of 30 hours of skilled labor and 20 hours of unskilled labor. Estimate the change inunskilled labor y that should be made to offset a 1-hour increase in skilled labor x so that the output will be maintained at its current level.