Find the number of square units bounded by the $x$-axis, the $y$-axis and the line $x+ y= 6$.
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
Find the number of square units bounded by the $x$-axis, the $y$-axis and the line $x+ y= 6$.
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
18
Find the number of square units bounded by the $x$-axis, the $y$-axis and the line $x+ y= 6$.
train