求高考难度的英文数学题

我有...很多啊...哈...^^算好了SCANE给我看吧...哈...我数学很差...

1.Demand Equation
The price P and the quantity X sold of a certain product obey the demand equation
x=-5P+500 0 less or equal P less or equal 20
上面这个是0小于或者等于P,P 小于或者等于20(因为不会打那符号)

a)express the revenue R as a function of X
b)what is the revenue if 15 units are sold
c)what quantity X maximizes revenue?what is the maximum revenue
d)what price should the company charge to maximize revenue?

2.Enclosing the MOst Area with a Fence
A farmer with 2000 meters of fencing wants to enclose a rectangular plot that borders on a straight highway.If the farmet doesnt fence the side along the highway,what is the largest area that can be enclosed?

3.Suspension Bridge
A suspension bridge with weight uniformly distributed along its length has twin towers that extend 75 meters above the road surface and are 400 meters apart.The cab