Yes you are on the right track with part a), although I get to four decimal places, 30.7313 and for part b 20.7313. I assume you merely have a typo for your part b) result. Perhaps it is only an error of rounding.
Estimate the area under the graph of f(x) = 5√x from x = 0 to x = 4
using four approximating rectangles and right endpoints. (Round your answers to four decimal places.)
(b) Repeat part (a) using left endpoints.
Δx = ( 4 - 0 )/ 4 = 1
R4 = 1( 5√1 + 5√2 + 5√3 + 5√4) = 30.7314
L4 = 1(5√0 + 5√2 + 5√3 + 5√3) = 20.7314
Am I on track with this? The answer above is marked incorrect on webassign.