Martha spent 6/2=<<6/2=3>>3 dollars.

Martha and Doris spent 6+3=<<6+3=9>>9 dollars.

There were 21-9=<<21-9=12>>12 dollars left in the cookie jar.

# Answer

12
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
There were 21 dollars in the cookie jar. Doris spent $6 from the cookie jar. Martha spent half as much as Doris. How much money, in dollars, was left in the cookie jar?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
12
There were 21 dollars in the cookie jar. Doris spent $6 from the cookie jar. Martha spent half as much as Doris. How much money, in dollars, was left in the cookie jar?
train