Question 797162
given that
anna is 12 years old
A=12---------equ:1
where A is age of anna
her mother is three times as old as anna
M=3A---------Equ:2
by substituting equ:1 in equ:2 we get
M=3*12
M=36
therefore the present age of mother is 36 years
let X be the no. of years before her mother four times as old as anna
therefore  4[A-X]=M-X----------EQU:3
by substituting A=12 and M=36 in equ:3 we get
4[A-X]=M-X
4[12-X]=36-X
48-4X=36-X
-4X+X=36-48
-3X=-12
3X=12
X=12/3
X=4
therefore 4 years ago mother four times as old as anna