Question 1188209
Draw this helps
the bottom will be 40-2x by 30-2x, and that will equal 900 in^2. x is the length of the side of the square.
1200-140x+4x^2=900 
4x^2-140x+300=0
x^2-35x+75=0
x=(1/2)(35+/- sqrt (1225-300)); sqrt 925=30.4
x=32.7 inches and 2.3 inches; 2.3 inches is the answer.
the sides will become 35.4 x 25.4=899.16 in^2.