Hey Ferne!
Multiplication is commutative and associative, so let's regroup these numbers so they're easier to multiply.
\(\rm (4\times10^4)\times(2\times10^3)=(4\times2)\times(10^4\times10^3)\)
Apply your exponent rule to the powers of 10, adding the exponents together, and multiply the 4 and 2,
\(\rm =(8)\times(10^{4+3})\)
We can drop the brackets as a final step,
\(\rm =8\times10^7\)
Hope that helps!
