Since the operation is a multiplication, the order in which we made the multiplications doesn't matter, so we can reoprder it:
[tex]5.4\times10^3\times1.2\times10^7=5.4\times1.2\times10^3\times10^7[/tex]
Now, we calculate each of them:
[tex]6.48\times10^{3+7}=6.48\times10^{10}[/tex]
