Question 10788
Let x = age of the daughter now.
y = age of Mrs. Black now.

x+8 = daughter's age in 8 years
y+8 = Mrs. Black's age in 8 years


Two equations are needed, since there are two unknowns:

Sum of the ages now is 56.
x+ y = 56


Mrs. Black will be twice as old as her daughter.
y+8 = 2(x+8)  Solve for y:
y +8 = 2x + 16
y+8-8 = 2x + 16-8
y = 2x + 8


Substitute into 
x+y = 56
x+(_____) = 56
x+ (2x +8)= 56
3x + 8=56
2x = 48
x= 16  Daughter's age now



x + y = 56
16 + y = 56
y = 40 =  Mother's age now


In 8 years, daughter will be 24.
In 8 years, Mother will be 48.  


Check is that in 8 years, mother will be twice as old as daughter.


R^2 at SCC