As 9 hundreds is 9thousands

I think one of these should be it

9,900 is 900+9000

as far as what place 100th place and 1000th place.

as far as amount of zeros 2 zeros and 3 zeros

as far as simplification of numbers 9*100 and 9*1000

something else I learned in middle school I think 9.0 * 10^2 and 9.0*10^3