Answer:
Roger works 30 hours and his brother works 50 hours
Explanation:
Let
x ---->the number of hours Roger works in a month
y ---->the number of hours his brother works in a month
step 1
Find out how much they earn per hour
5,400-3,240=$2,160 -----> amount earned by 20 hours of work
$2,160/20=$108 per hour
step 2
Find out how many hours each brother works in a month
Roger
108*x=3,240
x=3,240/108=30 hours
His brother
y=x+20
y=30+20=50 hours