Let the length of the rectangle be x units then the width = (210 - 2x) / 2
= 105 - x units
Area A = x(105 - x) = 105x - x^2
Finding the derivative:_
dA/dx = 105 - 2x = 0 for max/minm volume
x = 52.5
this is for a maximum area because second derivative is negative ( = -2).
width = 105 - 52.5 = 52.5
Dimension for maximum area = 52 1/2 * 52 1/2. ( The rectangle is actually a square).
