Answer:

Step-by-step explanation:
Let
c -----> the additional amount (in dollars) David will spend
we know that
The word " at most" in this context means "less than or equal to"
The amount David has spent plus possible additional amounts he will spend must be less than or equal to $39
so
The inequality that represent this situation is

solve for c
subtract 22 both sides


The maximum amount he could spend is $17
Umm.. I have to see the problems, we might not have the same textbooks so
2x+6 = 20
take 6 from both sides
2x = 14
divide by 2 on both sides
x = 7
P(x)=R(x)-C(x)
=(-0.5x²+800x-100)-(300x+250)
=-0.5x²+800x-100-300x-250
=-0.5x²+800x-300x-100-250
=-0.5x²+500x-350 (2)