# Applicaitions of cubics + quadratics look at this :p

1. A student wants to construct an open box with a base area 35 cm2 from a rectangular piece of cardboard measuring 9 cm by 7 cm.
Find x, where x cm is the length of the side of the square which must be removed from each corner of the cardboard.

this is what i did, i went (9-2x)*(7-2x)=35, then i get it in a form of a quad or cubic, then find the x-intercepts?

2. From a rectangular sheet of metal, ABCD, the part ABP is cut, and the area of the remaining part is 114 cm2.
Find the value of x.

i am totally lost i dont know what to do here

3. The demand, x units of a certain product is given by x = 400 - 0.25p per month
where p is the selling price per unit. The cost, $C, to produce x units is given by C = 9600 + 1200x a) Express p in terms of x. yeah this one i did. p=4 (400 - x) b) The revenue obtained is a result of selling a number of units at a certain price. Express the revenue, R, in terms of x. totally lost, do i just use the x= 400 - 0.25p , and sub p from previous example in? d) Determine the number of units that must be produced and sold each month : i) in order to break even i have to use the c= formula and find the x-intercepts? ii) if the profit is to be$300 per month.

totally lost here

c) Express the profit, P, in terms of x.

profit... how do i do that?