first step)
it is $ 100 * 3,5 % = 3,5 $ , then 100+ 3,5 = % 103,5 per week
total earnings per year
30000* 3,5 % = 31050
second step)
Now you must establish the following relation to determine the numbers of houses that you must sell on a week to obtain $ 31 050 in a year
1 house* $ 31050÷ $ 103 /week * 50 week = 6 house / week
now , to know the quantity of houses in 50 weeks, it is 6 houses * 50 weeks = 300 houses / 50 weeks, you must sell 300 houses in 50 weeks to earn $ 31050