Assume the age the girl an her sister is 2x, x years resoectively.
ATQ
(2x +5) (x+5) = 150
2x2 + 10x + 5x + 25 = 150
2x2 + 15x + 25 - 150 =0
2x2 + 15x - 125 =0
2x2 + 25x -10 x - 125 =0
x(x+25) - 5( x+25) =0
(x-5) (x+25)=0
x = 5 , x =-25 (negative age is not possible)
Present age of the girl is 10 years and her sister' age is 5 years.