K = Kevin's age
D = Daniel's age
K = 3D
K - 4 = 5(D - 4)
Plug in 3D for the K values in the second equation.
3D - 4 = 5(D - 4) Use the Distributive Property
3D - 4 = 5D - 20 Add 4 to both sides
3D = 5D - 16 Subtract 5D from both sides
-2D = -16 Divide both sides by -2
D = 8
Now, plug that D value into the original equation.
K = 3D Plug in the D value
K = 3(8) Multiply
K = 24
Finally, you can double check your math.
4 years ago, Daniel would've been 4 and Kevin would be 20, so Kevin would've been 5 times as old as Daniel. And 8 x 3 = 24.
So, Kevin is 24.
