They are inverses.
The easiest way to solve this is to take the g(x) equation and switch the g(x) with the x. Then solve for your new g(x). Since it looks just like f(x) after doing that, it is an inverse.
Split up the interval [2, 5] into

equally spaced subintervals, then consider the value of

at the right endpoint of each subinterval.
The length of the interval is

, so the length of each subinterval would be

. This means the first rectangle's height would be taken to be

when

, so that the height is

, and its base would have length

. So the area under

over the first subinterval is

.
Continuing in this fashion, the area under

over the

th subinterval is approximated by

, and so the Riemann approximation to the definite integral is

and its value is given exactly by taking

. So the answer is D (and the value of the integral is exactly 39).
I can't really can't see the picture to help you out