Application problem set.. Please help

I have a packet of application problems and i've done most of them except for the ones i really didn't get and it's due tomorrow. please help

1) One campus of Houston Community College has plans to construct a rctangular parking lot on land bordered on one side by a highway. There are 640 ft. of fencing available to fence the other three sides. Let x represent the length of each of the two parallel sides of fencing

a) Express the lenght of the remaining side to be fenced in terms of x.

b)state the domain restrictions on x.

c)Determine a function A that represents the area of the parking lotin terms of x.

d)Find the value of x that will give the maximum area and state the dimensions of the rectangle.

Any help at all would be greatly appreciated.