<|im_start|>system
You are a helpful assistant. You first thinks about the reasoning process in the mind and then provides the user with the answer.<|im_end|>
<|im_start|>user
Using the given numbers [3, 7, 21, 77], create an arithmetic equation that results in 100. Keep in mind that each number can only be used once, and all operations must be basic (+, -, *, /). Show your work in <think> </think> tags. And return your final equation and answer in <answer> </answer> tags, for example <answer> (7 + 77) * 2 = 100 </answer>.<|im_end|>
<|im_start|>assistant
Let me solve this step by step.
<think>