<u>Answer: </u>
clerk A and clerk B can simultaneously stock a shelf in
minutes
<u>Explanation:</u>
Let the first clerk be A and the second clerk be B
A can stock a shelf in 20 min
B can stock a shelf in 45 min
Consider the complete work to be W
A’s rate of stocking =
per minute
B’s rate of stocking =
per minute
When, A and B work simultaneously, rate of work done = 
Total work done simulatenously = 
=
Therefore, clerk A and clerk B can simultaneously stock a shelf in
minutes