The baldwin family walked four over five of a mile in four over nine of an hour. what is their unit rate in miles per hour?

a. four-ninths over four-fifths equals four over nine mile per hour
b. four-fifths over four-ninths equals one and four-fifths miles per hour
c. four-ninths over four-fifths equals one and four-fifths miles per hour
d. four-fifths over four-ninths equals four over nine mile per hour