find the variables
As this equation is presented there are an infinite number of possible values for x and y that will equal 5/2. X could equal 1 (2/2) and y could be 3/2. Or x could be 251/200 and y could be 249/200 (as just one of the many many values that would make this equation true).
What is needed is a second equation. In general you need the same number of equations as unknown variables to solve for each variable in algebraic expressions like this.