To do it:
Write down 15,000 as 15 kilos (15 × 103) and 0.000004 as 4 micros (4 × 10-6).
Multiply the precision parts and add the exponents, i.e. 15 kilos by 4 micros will be 60 milli, because 103 × 10-6 = 10-3.
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