Solving by Substitution

To use substitution, solve one equation for one variable, then plug that into the other equation.

From $x + y = 10$, you get $y = 10 - x$. Substitute into $x - y = 4$: $x - (10 - x) = 4$, which simplifies to $2x - 10 = 4$, so $x = 7$. Then $y = 3$.

Check: $7 + 3 = 10$ and $7 - 3 = 4$. Both equations are satisfied.