First you will have to use the equation length*width*height. The just plug in 4 for the height, then since the length is 4 times longer plug in 4x, and the width would just be x. SO your equation would be 4*4x*x=6400 ft^3. Then foil it out to get 16x^2=6400, then square root 6400 which will give you80, then divide by 16 so x=5 feet^3. That is your width but you length is 4 times that amount. So for length just do 4(5)=20 feet^3
