He has 4*3=<<4*3=12>>12 pregnant fish

They give birth to 12*20=<<12*20=240>>240 fish

# Answer

240
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
Mark has 3 tanks for pregnant fish.  Each tank has 4 pregnant fish and each fish gives birth to 20 young.  How many young fish does he have at the end?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
240
Mark has 3 tanks for pregnant fish.  Each tank has 4 pregnant fish and each fish gives birth to 20 young.  How many young fish does he have at the end?
train