How do I solve this?

Let f be bounded and integrable on [a,b]. Define the partition PN = {a, at N", . ba, .. at(6-a) .by, the N division of b,a into N equally sized intervals. Let Cj = a + ]( b-a) n be the right endpoint of the jth in- terval, and define the right Riemann sum RN(f ) = _if(x;) . a). Show that for any N, we have LPN (f) LPN (f) > Lp(f). c). Con- clude that limN -> LPN (f) and limN-> UPN (f) both converge to ff(x)dx. d). Use the squeeze theorem to see that limN- RN(f) = ( f(x)dx