If Lorna's brother wore green on 9 out of the last 21 days, we can calculate the rate of him wearing green as 9/21.
To estimate the number of days he would wear green in the next five weeks, we need to know the number of days in a week. Assuming there are 7 days in a week, there would be a total of 5 x 7 = 35 days in five weeks.
Using the same rate, we can calculate the expected number of days he would wear green by multiplying the rate by the total number of days in five weeks:
Expected number of green days = (9/21) x 35
Therefore, Lorna would expect her brother to wear green on approximately (9/21) x 35 = 15 days in the next five weeks.