<|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 numbers [21, 34, 45, 78], craft an equation that equals 99. Use basic arithmetic operations (+, -, *, /) and each number can only be used once, along with justify your reasoning for the steps used. Show your work in <think> </think> tags. Please return your final equation and answer in <answer> </answer> tags, for example <answer> (45 + 34) * (78 / 21) = 99 </answer>. <|im_end|>
<|im_start|>assistant
Let me solve this step by step.
<think>