The height of a rectangular box is 5. The length is 5 longer than fourfold the width. The volume is 420

the equation is ...

To find the volume, the equation is

L*H*W=V

You can now put you numbers in the equation

L*5*H=420

If is L is 5 longer than 4W, L=4W+5

So

(4x+5) * (5) * (x) = 420

Now you remove your 5

(4x+5) * (x) = 84

You now have (5x+5) = 84

5x=79

x=15.8