Answer:
Jamal will have made 12 more T-shirts than Sean on the 6th day.
Explanation:
1 day for Jamal - 6 T-shirts. 1 day for Sean - 4 T-shirts. 2 day for Jamal - 12 T-shirts. 2 day for Sean - 8 T-shirts. 3 day for Jamal - 18 T-shirts. 3 day for Sean - 12 T-shirts. 4 day for Jamal - 24 T-shirts. 4 day for Sean - 16 T-shirts. 5 day for Jamal - 30 T-shirts. 5 day for Sean - 20 T-shirts. 6 day for Jamal - 36 T-shirts. 6 day for Sean - 24 T-shirts. Number between 24 and 36 = 12.