**Answer:**

b.For each additional dollar paid to a tutor, we expect exam score to increase by 1.5 points, holding number of hours of sleep per week and number of study hours fixed.

**Step-by-step explanation:**

Hello!

For any multiple regression model, you can define the estimated slope as "the change or modification of the estimated average of Y when one of the explanatory variables increases one unit while the others remain constant.

In this example the dependant variable is:

Y: Exam score

And you have three explanatory variables:

X₁: salary of the teacher ($).

X₂: hours of sleep per week of a student.

X₃: number of study hours of a student.

The estimated model is ŷ= 65 + 1.5X₁ + 0.2X₂ + 0.5X₃

You need to interpret the estimated slope of the amount paid to the teacher b₁= 1.5

The units of the slope are units of Y by units of X, in this case, Y has no units so it is 1/$.

Then we can say that for every additional dollar paid to the teacher, the estimated mean score of the exam will increase by 1.5 1/$ while the weekly sleep hours and study hours remain constant.

I hope it helps!