we start with
5^21*4^11=2*10^n
5^10*5^11*4^11=2*10^n
5^10*20^11=2*10^n
5^10*20^10*20=2*10^n
100^10*20=2*10^n
10^10*10^10*2*10=2*10^n
2*10^21=2*10^n
n=21
Answer B
OA?
Testprep1
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