Answer:
1. Equation: 
2. Total pay if Henry sells 27 copies:
Step-by-step explanation:
1. The equation of the line in Slope-Intercept form is:

Where "m" is the slope and "b" is the y-intercept.
According to the information given in the exercise, his base salary is $2,100. So you can identify that:

Since he makes an additional of $90 for every copy of he sells, you can identify that:

Therefore, the equation that represents this situation is:

2. If he sells 27 copies, then:

Substituting this value into the equation, you get that his total pay would be:
