x = y + 1...so sub in y + 1 for x in the other equation
4x + 3y = -31
4(y + 1) + 3y = -31...distribute thru the parenthesis
4y + 4 + 3y = -31...subtract 4 from both sides
4y + 3y = -31 - 4....combine like terms
7y = - 35...divide both sides by 7
y = -35/7
y = - 5
now sub -5 in for y in either of the original equations to find x
x = y + 1
x = -5 + 1
x = -4
solution is (-4,-5)