we know that
a greater conveyor belt moves 100 pounds ------------> 5 minutes
so
Applying proportion
1-minute ---------> move 100/5=20 pounds
a smaller conveyor belt moves 100 pounds ------> 9 minutes
so
Applying proportion
1-minute --------> move 100/9 pounds
therefore
If both belts are used
then
1-minute --------> move 20+(100/9)=(180+100)/9=280/9 pounds
Applying proportion
Find out how long it takes to move 100 pounds
Simplify the fraction
45/14
Convert to a mixed number
45/14=42/14+3/14=3 3/14 minutes
The answer is 3 3/14 minutes