Pretend Daniel is x.
Kevin is 4 times as old so Kevin is 4x
4 years older is x+6
So 4x=x+6
Now simplify.
Subtract x from both sides, you're left with 3x=6
Divide both sides by 3 you get x=2
So Daniel is 2. Kevin is 8, which is 6 years older and 4 times older