Question

find the upper and lower bounds for definite integral sign, a=1, b=6, sqrt(x) dx. partitions are as follow: x0=1, x1= 3, x2=6 of the interval [1,6]

upper sum: 3sqrt(3) + 3sqrt(6)
lower sum: 3sqrt(3) + 3

but this is incorrect. can someone explain what i did wrong please