Since $10^x - 10 = 9990,$ we have $$10^x = 9990+10=10000.$$If $10^x = 10000,$ then $x=\boxed{4},$ since $10000$ ends in four zeroes.
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
If $10^x - 10 = 9990,$ what is $x$ equal to?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
4
If $10^x - 10 = 9990,$ what is $x$ equal to?
test