Algebra

the answer is 271404/131227

$\begin{cases}725x + 727y = 1500 \text{ --- }(1)\\729x + 7y = 1508\text{ --- }(2)\end{cases}$

Subtract (1) from (2) to get 

$4x - 720y = 8\\ x - 180y = 2\text{ --- }(3)$

Now, solve the system formed by equations (2) and (3) using method of elimination, and you will get $(x, y) = \left(\dfrac{271454}{131227}, \dfrac{50}{131227}\right)$

Therefore, x - y = $\dfrac{271404}{131227}$, as robloxDying suggested.

I think that that 7 in the 7y term looks incongruous.

I suspect a typo !