[tex]\left( 8 \times 10^{-5}\right)\cdot \left( 5 \times 10^{-6}\right)\\ \\ =\left( 8 \times 5\right)\cdot \left( 10^{-5} \times 10^{-6}\right)[/tex]
1) first do the integer part [tex]\left( 8 \times 5\right)=40[/tex]
2) then do the exponent part [tex]\left( 10^{-5} \times 10^{-6}\right)[/tex] = ???
3) Once you do the first two steps... adjust your answer to scientific notation...