A shoe salesperson sold 20 pairs of shoes for $640. A brown pair of shoes sells for $30 and a black pair for $35. How many brown pairs were sold? A. 12 B. 14 C. 15 D. 8

12 pairs

Step-by-step explanation:

Represent Brown with B and Black with A

So:

--- Pairs sold

--- Amount

Required

Solve for B (the brown pairs)

Make A the subject in the first equation

Substitute 20 - B for A in the second

Open bracket

Collect Like Terms

Divide both sides by -5

10% of increase is the final answer! : )