A new restaurant just opened up in your neighborhood. One soda costs $2.75, and five sodas cost $13.75. Is the cost a proportional or non-proportional relationship?

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

x = 4/9 *60/1 = 240/9 =  26,6 min. 

4/5 mile in 26,6 min.
1 mile   x min.

x = 1*26,6/(4/5) = 26,6 /(0,8) = 33,25 min. 

1 mile 33,25 min.
x miles 60 min.

 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