Question 635345
Let the square card board have length = x

#feet is cut from each corrner

so the length decreases by 6 feet.

new length = (x-6)

height = 3 ft.

Volume = (x-6)*(x-6)*3

(x^2-12x+36)*3=147

/3
x^2-12x+36 = 49

x^2-12x-13=0

x^2-13x+x-13=0

x(x-13)+1(x-13)=0

(x-13)(x+!)=0

x=13 OR -1

ignore negative 

the length is 13 feet