connie is 4 years older than carla. the sum of their ages is 28. how old is carla

Co=Ca+4      (1)

Co+Ca=28     (2)

Sub 1 into 2

Ca+4+Ca=28

2Ca+4=28

2Ca=24

Ca=12

sub back into (1)

Co=12+4=16

Carla is 12

Connie is 16

Carla is 12 years old and Connie is 16 years old