Question

D=100-2p, p is the price in dollars of the product and D is the number of products that can be sold at that price.

Answer 1

D=100-2p
P=price
D=products sold
in this case, the number of products you would want to sell is 75 so->
1)   75=100-2p             
2)   75+2p=100   
3)   100-75=2p
4)   25=2p
5)  25/2=p
6)  p=12.50