okay, so one way to do that is this:
Since the value of both fractions is the same (as is communicated by the equal sign), then we know that making them both equal to 1 will help us figure out the answer. So, if we say that 14/14 = 21/21, then we have now deduced that (x-11=14), and thus (14+11=x=25), and thus 25=x. Then, y+3=21, so we know that 21-3 will = y, which thus equals 18.
So then x=25 and y=18.
i hope this helped :)