we know that volume of the box=length*width*height
length=2x+2 width=x-2 height=x
perimeter of the box=2*[length+width] 90=2*[2x+2+x-2]----> 90=2*3x-----> 6x=90----> x=15 cm so length=2x+2----> 2*15+2----> 32 cm width=x-2------> 15-2----> 13 cm height=x------> 15 cm