We know that
• Large shelves require 40 pounds.
,
• Small shelves require 30 pounds.
,
• The company has only 400 pounds of metal.
,
• The selling price of each large shelf is $80.
,
• The selling price of each small shelf is $49.
First, let's make a table with the given data of the problem, this will help you organize it.
From the given information, we can define the following constraints.

These constraints form the following region:
To find the maximum income possible, we have to evaluate the income function at (0,13.333) and (10,0).

Observe that we formed the income function using the table above. Now, let's evaluate it at each point.

Therefore, they would have to sell 10 large shelves to reach a maximum income of $800.