How do you do these problems, and whats the answer to this one?

(7.3x10^-5)(5.8x10^2).....since we're just multiplying, we have

[ 7.3 * 5.8 ]  * [ 10^-5  *  10^2]  =    

42.34 *  10^-3

In scientific notation, it would be :

4.234 x 10^-2