Answer
a) The mowed portion is the field (total area) minus the habitat (middle square).
b) $4x(b-x)$
Work Step by Step
a) We can obtain the area of the mowed portion by subtracting the area of the middle square $(b-2x)^2$ from the total area ($b^2$).
b) $b^2-(b-2x)^2=b^2-(b^2-4bx+4x^2)=4bx-4x^2=4x(b-x)$
