Answer: 9.75 x 10^11
Step-by-step explanation:
Product means multiply so we're solving 2.5x10^-15 x 3.9x10^26.
Since multiplication can be done in any order, we can do this in two stages:
(2.5x3.9) x (10^-15x10^26)
First 2.5 x 3.9 = 9.75
Secondly we have 10^-15 x 10^26. The bases (10) are the same, so all we need to do is add the powers, -15 + 26 = 11. So 10^-15 x 10^26 = 10^11
Finally we put them back together, and have 9.75 x 10^11