Answer
2.4$\times$$10^{10}$
Work Step by Step
(3$\times$$10^{5}$)$\times$(8$\times$$10^{4}$) = (3$\times$8)($10^{5+4}$) = 24$\times$$10^{9}$ = 2.4$\times$$10^{10}$
If you add a decimal to the answer from left to right, then you add 1 to the exponent, so that is why the power changed from 9 to 10 as you added an extra decimal.
