Acamera and case together cost 110. if the camera cost 100 more than the case, how much does the case cost?

X=cost of camera
y=cost of case

x+y=110

camera is 100 more than case
x=100+y

subsitute 100+y for x

100+y+y=110
100+2y=110
minus 100 both sides
2y=10
divide both sides by 2
y=5

sub back
x=100+y
x=100+5
x=105
the camera costs $105

the case costs $5