Answer:
3.81 centimeters per month
Step-by-step explanation:
We know that 1 inch is equal to 2.54 centimeters, so to convert 1.5 inches per month to centimeters per month we will use the proportion 2.54 cm / 1 in.
Therefore, 1.5 inches per month is equal to:

So, the plant root grows 3.81 centimeters per month