Riding a century

How far do people generally ride before riding a century? I ask because my
ride this Sunday is 100km, but I can also ride 100 miles. I'm thinking of
riding the 100 miles instead of the 100km. My long rides have been 55
miles (last week), 50 miles (the week before), 45 miles (two weeks ago)...
I only ride about 4 days a week, the other 3 days being about 20 miles a
day. Is this enough riding to ride 100 miles?

Thanks.

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Bob M in CT
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