Question 102423
If the function is P(x)=2.25x-7000

A.) For every instance of x, you must plug in 2000 units since x is equal to the units sold.  Therefore, P(2000)=2.25(2000)-7000
2.25(2000)=4500-7000=-$2500 profit.

B.)For every instance of x, you must plug in 5000 units since x is equal to the units sold.  Therefore, p(5000)=2.25(5000)-7000
2.25(5000)=11250, then subtract 7000 to get a profit of $4250

C.)To get the break-even point you must set the units to x.
Your equation is P(x)=2.25(x)-7000=0
2.25(x)=2.25x-7000=0  Then add 7000 to the other side.
2.25x=7000 divide now to get the x variable alone
x=7000/2.25 
x=$3111.11
Plug it into the original function to verify your work.
P(3111.11)=2.25(3111.11)-7000
2.25(3111.11)=7000 then subtract 7000 
7000-7000=0 or your break-even point

I hope this helps...however, please verify that the function p(x)=2.25x-7000 is the correct function given by your book.  If you have any further questions let me know.