According to the question if we take one number as a M and 3 more than other represent m+3
so the equation will be : m+(m+3)=-13
2m+3=-13
2m=-16
m=-8(one number)
to get another number plug in -8 for m and that gives us -8+3=-5
prove if we pluged in all than we get the same result,-8-5=-13
that was the prove of that math hopefully you get it