hi this is a Riemann sum q:

Find U, the Riemann Upper Sum for f(x) = x2 on [0,2], using 4 equal sub-intervals

i know that n=0.5 so i thought the upper limit would be 0.5^2+ 1^2+1.5^2+2^2 which gives 7.5 but the answer is 3.75 so could someone please explain why this is the answer?

cheers