Answer: The required time taken to assemble 9 shelving units is 4 hours 30 minutes.
Step-by-step explanation: Given that we can assemble a shelving unit every 30 minutes.
We are to find the time taken to assemble 9 shelving units at the same rate.
We will be using the UNITARY method to solve the given problem.
We have
Time taken to assemble 1 shelving unit = 30 minutes.
So, time taken to assemble 9 shelving units is given by

Thus, the required time taken to assemble 9 shelving units is 4 hours 30 minutes.