The given expression is
5.1 x 10^6 x 2.3 x 10^6
We would apply the law of exponents which is expressed as
a^b x a^c = a^(b + c)
By applying this, we have
5.1 x 2.3 x 10^6 x 10^6
= 11.73 x 10^(6 + 6)
= 11.73 x 10^12