12. (6 points) Find the area of the region bounded by the curve and the x-axis from x = 0 to x = 2. Here f(x) = e- ex. f(x) 13. (5 points) Find the critical numbers and open intervals where the function increases and where it decreases. y = xex-3x 14. (6 points) Suppose v(t) = t2 + 2et , and s(0) = 15. Find a(t) and s(t). 15. (6 points) Use a definite integral to find the area between the x-axis and f(x) over the interval. Check first to see if the graph crosses the x-axis in the given interval. f (x) = x3 , [-5, 3]