Find the units digit of $29 \cdot 79 + 31 \cdot 81$.
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
Find the units digit of $29 \cdot 79 + 31 \cdot 81$.
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
2
Find the units digit of $29 \cdot 79 + 31 \cdot 81$.
train