Rob is two times as old as jake. three years ago the sum of their ages was 21 years. find their present ages?

Suppose Rob's age is X and Jake's age Y

Since Rob is two times as old as Jake, X = 2Y

Since Three Years ago the sum of their ages was 21,

X + Y = 21 + 6 This is true because it was three years ago, so they both got older by 3 years

You plug in X to the second equation to fin 2Y + Y = 21 + 6 which is 3Y = 27, so Y = 7 Then, you plug this into the first equation and find that X = 14

So Rob is 14 and Jake is 7

Hope this helps :)