Question

One number is 5 more than another number. their sum is −15 . what are the numbers?

Answer 1

x=5+y
x+y=-15

subsitute 5+y for x

5+y+y=-15
5+2y=-15
minus 5 from both sides
2y=-20
divide both sides by 2
y=-10

sub back
x=5+y
x=5-10
x=-5

the numbers are -10 and -5