Question

(8.4 times 10 to the 2 power)(2.5 times 10 to the 6 power)

Answer 1

(8.4 * 10^2) (2.5 * 10^6)
associative property -> we can multiply these in whichever order we want
8.4 * 2.5 * 10^2 * 10^6
21 * 10^8
if your instructions said to put the answers in scientific notation, however, we are not done here
21 * 10^8
2.1 * 10 * 10^8
2.1 * 10^9

Answer 2

$8.4*10^2*2.5*10^6\to\boxed{21*10^8}$