Jeremy=x
Older sister=x+5
younger sister=x+5-9 or x-4
x+(x+5)+(x-4)=49
combine like terms
3x+5-4=49
3x+1=49
subtract 1 from both sides
3x=48
divide both sides by 3
x=16
Jeremy=16
Older sister=16+5=21
younger sister =16-4 or 16+5-9=12
J=16
OS=21
YS=12