Question 130
If we use R for Ralph and F for Frank, the initial relationship between their ages is R = 4F

Ralph's age in twenty years will be R + 20, or his age now plus 20 years.

Frank's age will likewise be F + 20 in twenty years

Therefore the second equation we can write is 

--> (R + 20) = 2(F + 20)

If we then substitute 4F for R in the second equation 
--> (4F + 20) = 2(F + 20)

We then distribute the 2:

--> 4F + 20 = 2F + 40
Subtract 20 from both sides;

--> 4F + 20 - 20 = 2F + 40 - 20 
--> 4F = 2F + 20

Subtract 2F from both sides

--> 4F - 2F = 2F + 20 - 2F
--> 2F = 20

Divide both sides by 2;

--> 2F/2 = 20/2
--> F = 10

When we substitute 10 for F back into the original equation (R = 4F);

--> R = 4*10 = 40

Hence Frank is now 10 and Ralph is 40
Twenty years from now, Frank will be 30 and Ralph will be 60, or twice Frank's age

So the answer is F = 10 and R = 40