The break even point is when profit is equal to zero, or in this case when p(x)=0
4x^2-28x+40=0
4(x^2-7x+10)=0
4(x^2-2x-5x+10)=0
4(x(x-2)-5(x-2))=0
4(x-5)(x-2)=0
So the break even points are when x=2 and 5, which is when 2000 and 5000 units are sold.
For 80 guests you will need 80/10 = 8 times more than for 10 guests:
8*9.50 = $76
Refreshment for 80 guests costs $76.
X-2=6x+18
-x -x
-2=5x+18
-18 -18
-20=5x
x=-4
Yours d+v=45minutes and roommate d+v=100minutes
#8 you do 360= 112+136+x... then you solve for x. X=112. Now you divide this by two since it is an inscribed angle. For #9 I have this very simplified work in the picture. Sorry I did not do #10