Answer: I think the answer is 4 because usually when you find the rate of something it means you divided the two numbers or however many numbers you have... So, 12 divided by 3 is 4... So, 4 hours for each lawn she mows... or something like that... So, 4 lawns per hour...
Final answer is 4 lawns per hour... If this isn't the correct answer i am very sorry... Stay safe and have a great weekend!!! :D