Question 1154023
Basic formula is 
Profit = Revenue - Cost

Part 1)
Cost = $400 per month (the rental cost)
Let's assume that a month is 4 weeks, since the profit has to be calculated weekly.
So weekly cost = $400/4 = $100 (this is an approximation, in many rental offices the weekly rent would not be 1/4 of the monthly rent, but it is close)

Revenue for 1 week with 15 students at $40 per student = 15 * 40 = $600

So profit for 1 week = Weekly Revenue - weekly cost = $600 - $100 = $500

Ans = <b>$500</b>

Part 2)
If she has to make a profit of $800, her revenue has to be $800 + $100 = $900
(Revenue = Profit + cost)
To make $900 at $40 per hour, she has to tutor 900 / 40 = 22.5 or 23 students.
(Since no. of students cannot be a fraction, we round it up to the next higher number)
Ans = <b>23</b>