Answer:
B. 10
Step-by-step explanation:
x + y = 21
xy = 110
Rewrite first equation. x + y = 21 becomes y = -x + 21
Now substitute this new equation in the second equation.
x(-x+21) = 110
-x^2 + 21x - 110
Divide by -1
x^2 - 21x + 110
(x - 10)(x - 11)
x = 10, 11
10 is less, so the youngest daughter is 10