Answer:
16 y.o
Explanation:
say rebecca = x
therefore, cynthia = 6x
when rebecca ages 6 years (x+6), cynthia will be 3(x+6) years old
since cynthia's original age + 6 will be equal to the new expression of her age after 6 years
3x + 18 = 6x + 6
18 = 3x + 6
3x = 12
x = 4
as cynthia = x + 6 (NOTE: AT THE BEGINNING) her original age was 10.
however after 6 years she's 16