remember that multiplication is commutative, so we can multiply in whatever order we feel like, let's choose a convenient one.

recall that when we multiply numbers of the same base, we add the powers, when we divide numbers of the same base, we subtract the power from the base in the denominator from the one in the numerator. let's see how all this works out:

(2.3 x 10^4)(3 x 10^-2)..........2.3 x 3 x 10^4 x 10^-2

------------------------..=..-------------------------- ..reorder the terms

.......5 x 10^-6..............................5 x 10^-6

...........................................6.9 x (10^(4-2))

....................................=..-------------------- .....add the powers of 10

.............................................5 x 10^-6

...........................................6.9 x 10^2

....................................=..---------------

.............................................5 x 10^-6

.........................................6.9..........10^2

....................................=..-----..x..--------- ..separate terms

..........................................5...........10^-6

....................................= 1.38 x 10^(2-(-6)) ...subtract powers of 10

....................................= 1.38 x 10^8