math

= 6.4 / 4   x  10^(-4)/10^6   =  1.6 x 10^(-4 -6)  = 1.6 x 10^(-10)

Thanks ElectricPavlov, your answer is spot on - yes i know that you know that :)

what is (6.4 times 10 to the negative 4 power) divided by (4 times 10 to the positive 6 power)

\((6.4*10^{-4})\div (4*10^6)\\ =\frac{6.4*10^{-4}}{ 4*10^6}\\ =\frac{1.6}{ 10^6*10^{+4}}\\ =\frac{1.6}{ 10^{10}}\\ =1.6*10^{-10}\)