We need to write out algebraic equations to describe the information we have, then solve them using substitution.
We will define length as a and width as b.
we know that a x b = 1600 cm3 (area = length x width)
So, we can substitute the vaule 4b for a in the first equation:
4b x b = 1600
we can simplify to 4b2 = 1600
divide both sides by 4:
b2 = 400
take the square root of each side:
b = √400
So we know the width = 20
length = 4 x width = 80