For the function, do the following. f(x)=x from a = 3 to b = 6. (a) Approximate the area under the curve from a to b by calculating a Riemann sum using 6 rectangles. Use the method described in this example rounding to three decimal places. square units (b) Find the exact area under the curve from a to b by evaluating an appropriate definite integral using the Fundamental Theorem. square units