The total number of shirts for all his kids is 3 * 3 = <<3*3=9>>9 shirts.

The total number of needed buttons is 9 * 7 = <<9*7=63>>63 buttons.

# Answer

63
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
Jack sews 3 shirts for each of his 3 kids. He sews 7 buttons in each shirt. How many buttons must Jack use for all the shirts?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
63
Jack sews 3 shirts for each of his 3 kids. He sews 7 buttons in each shirt. How many buttons must Jack use for all the shirts?
train