Answer:
Explanation:
You should set this up as an y = mx + b equation. Since 300 is her final number, that will be your y value. She started with 100, so that will be your b value. 20 is the number related to the variable you don't know so that will be your m.
300 = 20x + 100
-100 -100
200 = 20x
divide both sides by 20
10 = x