Question

What is the answer for Chris' age and Mary's age?

Answer 1

M=mary's age
c=chris's age

m is 4 younger than 3 times chris
m=-4+3c
m=3c-4

mary's age 3 years ago (m-3) is equal to chris age in 9 years (c+9), find c and m

m-3=c+9

we got
m=3c-4
sub 3c-4 for m in other eqution
3c-4-3=c+9
3c-7=c+9
minus c both sides
2c-7=9
add 7 to both sides
2c=16
divide both sides by 2
c=8

sub back
m=3c-4
m=3(8)-4
m=24-4
m=20


mary=20
chris=8

Answer 2

Mary = M   Chris = C
M = 3C-4
M-3=C+9 -->  M=C+12
3C-4=C+12
2C=16
C=8
M=3C-4   --> C=8
M=3(8)-4
M=24-4
M=20

Mary is 20, and Chris is 8