Asalesperson works 40 hours per week at a job where she has two options for being paid. option a is an hourly wage of 23. option b is a commission rate 5% on weekly sales. how much does she need to sell this week to earn the same amount with the two options

Let's start with option A --> $23 per hour x 40 hours = 23 x 40 = 920 = $920

That means we have to find how many $ x 5% = $920 

We'll call our unknown amount: "B", so B x 0.05 = $920

To find B you have to get ride of everything on its side:
(B x 0.05) / 0.05 = 920 / 0.05 > we have to do the same operations on each side.
Now we have B = 920 / 0.05 > B = $18,400
The salesperson must sell $18,400 in order to earn the same amount as the first option.