A plant is 58 centimeters tall, and it grows one centimeter each month.

How tall is it after 21 months.

This means that after 21 months, the plant would have grown 21 centimeters more (because 1 cm every month, 21 months, 1 * 21 = 21). Add them:

58 + 21 = 79 centimeters.

79 centimeters

Step-by-step explanation:

Identify what you know:

1) The plant is 51 centimeters tall

2) The plant grows 1 cm more each month

So, we can create a formula to find the answer, where x equals the number of months after the plant was 58 cm tall.

58 + (1 times x) = height of plant

58 + (1 x 21) = ?

58 + 21 = ?

? = 79 cm