Product Mix Problem

Your company grows two types of plants, A and B (e.g., roses and begonias).

Both plant types require two types of fertilizer throughout the growing season, Fertilizer 1 and Fertilizer 2.

A single plant A will require 2 pounds of fertilizer 1 and 1 pound of fertilizer 2.

A single plant B will require 1 pound of fertilizer 1 and 2 pounds of fertilizer 2.

Your distributer has 4000 pounds of fertilizer 1 and 5000 pounds of fertilizer 2 available for delivery at the beginning of the season.

You know that every plant A you grow will generate $2.25 profit, and every plant B you grow will generate $2.60 profit.

1.How many of each plant should you grow if you want to maximize profit for the season?

2.What amount of change in profit for plant A and plant B will change your decision about product mix?

3.How much will you be willing to pay for additional amounts of fertilizer?

4.If your fertilizer storage capacity is 8000 pounds, what is your new product mix, and how much of each fertilizer should you order?What would you be willing to pay for additional storage capacity?

I need help with number 4. I am able to get 1,2,3 but I am unsure as how to tackle number 4. Could you help me out? Thank you