Question

Two numbers, x and y, have a sum of 8 and a difference of –14.

Answer 1

$x + y = 8 \\ x - y = - 14 \\ adding \: both \: the \: equations \\ 2x = - 6 \\ x = - 3 \\ \\ - 3 + y = 8 \\ y = 11$

there you go :)