math
posted by Noelle .
Dorthy is 6 years older than Ricardo. The product of their present age is twice what the product of their ages was 6 years ago. How old is Dorthy?

Ricardo's present age  x
Dorothy's present age  x+6
product of their present ages = x(x+6)
6 years ago:
Ricardo x6
Dorothy x
product of their ages then = x(x6)
x(x+6) = 2x(x6)
solve for x, sub into x+6 
Let D=age of Dorthy.
" Dorthy is 6 years older than Ricardo. "
Age of Ricardo = D6
"The product of their present age"
D(D6)
"is twice what the product of their ages was 6 years ago"
=2*((D6)*(D66))
Thus
D(D6) = 2*((D6)*(D12))
Simplify and solve for D and reject the solution of D=6 because it is a trivial solution. Check the answer by substitution into problem data.