If Minnie mounts three more horses per day than there are days in a week, then Minnie mounts 7+3=<<3+7=10>>10 horses per day.
Twice as many horses per day as Minnie mounts is 10*2=<<10*2=20>>20 horses per day.
If Mickey mounts six less than twice as many horses per day as does Minnie, then Mickey mounts 20-6=<<20-6=14>>14 horses per day.
Since there are 7 days in a week, then Mickey mounts 7*14=<<7*14=98>>98 horses per week.
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