Profit P=R-C where R is revenue from services and sales and C is cost.
In a month how many students do they average? If we say there are 4 weeks in a month we are talking of 28 days. But if we use a year as the basis of calculation, 1 year=12 months=52 weeks.
So we can work out the profit per year and then divide by 12 to find out the average monthly profit.
In one year the rent is 12*200=$2400.
In one year they average 52*10=520 students which brings in revenue of 520*15=$7800.
So the profit for a year is 7800-2400=$5400.
The profit per month is 5400/12=$450.
If we had calculated on a monthly basis and used 4 weeks=1 month, the profit would have come out as $400 a month.