1: because it is a rectangular you can find the area by using this equation:
A = b*h
2: So you know that 180 feet is for three sides of the garden:
180 = 2h+b --> b = 180-2h
and you also know that:
A = b*h = (180-2h)*h
If you differentiate (solve A'=0) for this equation, you will find that h=45.
Therefore b must be equal to 90.
3: the greatest area is therefore A = 90*45 = 4050
I hope that helped.
