Answer:
Step-by-step explanation:
p + c = 110
p = c + 100
c + 100 + c = 110
2c + 100 = 110
2c = 110 - 100
2c = 10
c = 10/2
c = 5 .......cost of the phone case
p = 5 + 100
p = 105 <=== cost of the phone
= -6 2/3
(-4 , -3)