Monte carlo application

If f(x) is continuous and increasing on [1,4]

f(1) = 1

f(4) = 3

The inverse function of f(x) is denoted g(y) on [1,4] (g(y) is also continous and increasing on [1,3]

If we assume that a random # generator generates pairs of numbers (x,y) where 1<= x<=4 and 0<=y<=3.

If 10,000 of these pairs are generated and 9025 pairs are such that for the given (x,y), we have u <= f(x).

I need to estimate the integral f(t)dt over (1,4) using this. Can anybody walk me through the process?