Answer :
y beeing her sister age
x being her age
y=x-4
140=x+y
140=x+x-4
140=2x-4
144=2x
72=x
She is 72 and her sister is 68
x being her age
y=x-4
140=x+y
140=x+x-4
140=2x-4
144=2x
72=x
She is 72 and her sister is 68