10^4 is another way to write 10⁴ = 10·10·10·10 = 10,000.
Essentially, the exponent tells you how many places to the right of the leading digit the decimal point lies (here, the number of zeros in the number).
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<em>Comment on the answer choice</em>
The appropriate answer depends on what you mean by your problem statement. Some microscopes magnify 40 times; others magnify 10,000 times, so we cannot tell the appropriate answer using our knowledge of microscopes.
