so basically we only use the associative property of multiplication and one of the laws of exponents
associative=a(bc)=(ab)c
also law of exponent=a^x times a^y=a^(x+y) so
(2 times 10^-3) times (3 times 10^4)
associative
2 times 10^-3 times 3 times 10^4
2 times 3 times 10^-3 times 10^4
law of exponents
10^-3 times 10^4=10^(-3+4)=10^1
2 times 3=6
the answer is 6 times 10^1 or (6*10^1) aka 60