Final answer:
The total number of t-shirts sold in this case is 100.
Step-by-step explanation:
To find the total number of t-shirts sold, we need to multiply the number of t-shirts sold by each member by the number of members. In this case, each member sells 5 t-shirts and there are 20 members. So the total number of t-shirts sold is 20 * 5 = 100. Therefore, the correct answer is b) 100.