You would have to move the decimal place #cancel(5)#4 units to the left so that it is after a significant figure (usually between the top two significant figures but as there is only one it is better to put it after). As the significant figure is greater than a whole number it will be to the power of positive #cancel(5)4#.
Hope this helps!
RW: Scientific notation requires a number to be written as a real number between 1 and 10 multiplied by the appropriate power of 10. Hence #20,000 =2* 10^4#