Final answer:
The plant root is growing 3.81 centimeters per month.
Step-by-step explanation:
To convert inches to centimeters, we need to use the conversion factor of 2.54 centimeters per inch. In this case, the plant root grows 1.5 inches per month. So, to find the growth in centimeters, we multiply 1.5 inches by 2.54 centimeters per inch. The result is 3.81 centimeters.