so walked 4/5 mile in a 4/9 h so just use the rule of 3 simple
60 minutes ------ 1 hour
x min. ----------- 4/9 h
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x = 4/9 *60/1 = 240/9 = 26,6 min.
4/5 mile -------in 26,6 min.
1 mile -------- x min.
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x = 1*26,6/(4/5) = 26,6 /(0,8) = 33,25 min.
1 mile ..... 33,25 min.
x miles ----- 60 min.
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x = 60/33,25 = 1,8 miles
so their unit rate in miles per hour will be 1,8 miles / hour
hope this will help you.