<span>4x(5y-x)-5y(4x-y)=20xy-4x^2-20yx+5y^2=-4x^2+5y^2=5y^2-4x^2</span>
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.
for 5 lb. bag = $6.76
so, for 1 lb. bag = 6.76/5 = $1.35
So, unit prize is $1.35 per pound.
90 is the answer to that question
