evaluate 4x^2+y by breaking into four congruent subrectangles and evaluating at the midpoints, 1=<x<=5 0=<y<=2

When i setup the rectangles these are my coordinates:

(1,1/2),(1,3/2),(3,1/2),(3,3/2) and delta A = 2

My answer comes out to be 168

When i integrate the function i get 338.6

The question then asks to compute the (riemann answer - the integral) which will be negative so im not sure if i did the riemann correctly can someone check my work and give some feedback