The answer is B:40 hours. You take 200 divided by 20 to get 10 (the amount of 20 page sections he needs to read) and then multiply 10 by 4 (the speed he reads).
If each member sells the same number of raffle tickets, then 13r would show that each of the 13 members will have sold <em>r</em> raffle tickets each. The expression is multiplication.
