Answer:
Denise = 16
Sister = 10
Step-by-step explanation:
D=denise
S=sister
Eq 1) D=S+6
Eq 2) D-8 =4S-8
replace D with S+6 in Eq 2
(S+6)-8 = 4S -8
S-2 = 4S -8
add 8 to both sides
S+6 =4S
subtract S from both sides
6 = 3S
divide both sides by 3
2 = S ( this is the sister age 8 years ago )
2+8 = 10 current age
plug that into Eq 1)
D = 10 +6
D=16 (Denise's current age)
so
Denise = 16
Sister = 10
if you subtract 8 from each , then there ages 8 years ago would be
Denise =8
Sister = 2
and 2*4 = 8
this checks
