A gym employee is paid monthly. After working for 3 months,he had earned $4,500. To determine how much money he will make over a six-month period,he created the table below.

1. If he continues to earn at the same rate, how much will he have earned after working 5 months?

2) After how many months will the gym employee have made $19,500?

3) Write an equation to represent the constant of proportionality.