1. I grew 3 cm a year.

Question

2. I grew by 3 cm a year.

(Does #1 mean #2? Is 'by' omitted before 3 cm? Then 'grew' is an intransitive verb. If not, 'grew' is a transitive verb.)

Answer 1

Both are correct.

Sra

Answer 2

Both statements suggest that — in the past — you grew 3 cm each year. If the growth was only in one year, you could designate the year:

"I grew 3 cm last year."

I hope t his helps a little more. Thanks for asking.