[0.2/0.24 Points] DETAILS PREVIOUS ANSWERS Let f(x) = -x2 + 8x. (a) Find the derivative f' of f by using the definition of the derivative. Show your work by completing the four-step process. (Simplify your answers completely for each step.) Step 1: f( x + h ) = -x2 - 2xh - h2+ &x+ 8h Step 2: f(x + h) - f(x) = -h( 2x + h-8) (Hint: Factor completely.) Step 3: f( x + h) - f(x) -2x -h+8 h Step 4: f ' (x) = lim f( x + h ) - F(x ) -2x + 8 h - 0 h (b) Find an equation of the tangent line to the graph of fat the point (3, 15). Give your answer in the slope-intercept form. X