In andrew’s furniture shop, he builds bookshelves and tables. each type of furniture takes him about the same time to make. he figures he has time to make at most 18 pieces of furniture by this saturday. the materials for each bookshelf cost him $20.00 and the materials for each table cost him $45.00. he has $600.00 to spend on materials. andrew makes a profit of $60.00 on each bookshelf and a profit of $100.00 for each table. how many of each piece of furniture should andrew make to maximize profit?

Given:
Cost to build a bookshelf = $20
Cost to build a table = $45
Amount available to spend = $600

Let x =  number of bookshelves built.
Let y =  number of tables built.

The total number of bookshelves and tables =  18.
Therefore
x + y = 18.
 That is,
 y = 18 - x                    (1)

The total amount available to build x bookshelves and y tables = $600. Therefore
20x + 45y = 600
That is (dividing through by 5),
4x + 9y = 120            (2)

Substitute (1) into (2).
4x + 9(18 - x) = 120
4x + 162 - 9x = 120
-5x = -42
  x = 8.4
From (1),obtain
 y = 18 - 8.4 = 9.6

Because we cannot have fractional bookshelves and tables, we shall test values of x=8, 9 and y=9,10 for profit

Note: The profit is $60 per bookshelf and $100 per table.
If x = 8, then y = 18-8 = 10.
The profit = 8*60 + 10*100 =  $1480

If x = 9, then y = 18-9 = 9.
The profit = 9*60 + 9*100 = $1440

The choice of 8 bookshelves and 10 tables is more profitable.

8 bookshelves and 10 tables.