Except there are values you want to substitute into the expression, this is what your answer looks like:
If you want me to solve for "Y" then, the answer will be,

ir if you want me to solve for "X" instead then the answer will be,

640 acres / 1 mi^2
<span>7.5 mi^2 (640 acres / 1 mi^2) </span>
<span>= 4,800 acres </span>