Find the point on the graph of f where the tangent line to

Question

Question: Let f(x) = x² + 6x.

a. Find the derivative f' of f.

b. Find the point on the graph of f where the tangent line to the curve is horizontal. Hint: Find the value of x for which f'(x) = 0.

c. Sketch the graph of f and the tangent line to the curve at the point found in part (b).