Let's use E to represent Emily
And use A to represent Amy.
So, E = 4
A = 12 come from (4 x 3)
These numbers are a factor of 4, so the easy way is to try to add each age wit 4, so 4 years later :
E = 4 + 4 = 8 years Old
A = 12 + 4 = 16 years old . . . .(Amy is 2 times older than Emily)
So the answer is 8 years old
