Question 817693
let father's age be x
daughter's age be y

mother's age = z

(x+y+z)/3= 35

x+y+z=105
z= 105-(x+y)

15 years hence 

105-(x+y)+15 = x+y

120-x-y=x+y

2x+2y=120
/2
x+y=60
z= 105-60
z= 45 mothers age