Rachel works at a bookstore. On Tuesday, she sold twice as many books as she did on Monday. On Wednesday, she sold 6 fewer books than she did on Tuesday. During the three days Rachel sold 19 books. Create an equation that can
be used to find m, the number of books Rachel sold on Monday.
Equation:

m = 5

Step-by-step explanation:

On Tuesday, she sold twice as many books as she did on Monday. An equation is now formed from this:

I Tu = Mo * 2

On Wednesday, she sold 6 fewer books than she did on Tuesday. An equation is now formed from this:

II We = Tu - 6

During the three days Rachel sold 19 books. An equation is now formed from this:

III Mo + Tu + We = 19

The task says that you should just use one equation to find out how many books were sold on Monday. So take the last equation and replace Tu and We with terms in which Mo occurs.

Substitute equation I into equation III:

IIIa Mo + Mo*2 + We = 19

Replace Tu in Equation II with Equation I:

II a We = Mo * 2 - 6

Substitute equation IIa into equation IIIa:

IIIb Mo + Mo * 2 + Mo * 2 - 6 = 19

Now the equation is converted to Mo (Mo = m):

m + m * 2 + m * 2 - 6 = 19   | + 6

m + 2 m + 2 m = 25

5 m = 25                              | : 5

m = 5