(5x10^2)x(5.6x10^4)
Online, "*" is used to indicate multiplication, so it will not be confused with "x" as an unknown.
Assuming all your x's indicate multiplication:
(5*10^2)(5.6*10^4) = 28 * 10^6
Assuming all your x's indicate multiplication:
(5*10^2)(5.6*10^4) = 28 * 10^6