do you know the laws of exponents?
for example, that x^m/x^n = x^(m-n) ?
anyway, we do this by a method we call "cancelling", actually i dont know if that's the official name for it, but hey.
so when we are given a rational function (a function that is a fraction, as in one function over another), we look what we can cancel in the functions by finding common factors.
so given (4x^2y)/(14xy^2)
we see that we have x's in the top as well as the bottom, we have y's in the top as well as the bottom, and we have multiples of 2 in the top as well as the bottom.
we cancel by dividing the common factors (in this case: 2, x, and y) into what we can to simplify.
we say 2 into 4 goes 2 times, so we cross out the 4 and write 2, at the same time, we say 2 into 14 goes 7 times, so we cross out the 14 and write 7. similarly we say x into x^2 goes x times and x into x goes 1 time. so we cross out the exponent 2 on the x in the top and cross out the x in the bottom completely, and so on. below is what it looks like when we do it. a similar process is used to simplify 18/36