Which of the following describes a unit rate a 16 pounds per 10 inches be 7 hours per day see 30 miles per hour or d30 fish per 10 gallons

The "unit rate" is the rate having 1 unit in the denominator:
  C. 30 miles per hour


Usually a "unit rate" is one with different units in the numerator and denominator. Selection B has one unit (day) in the denominator, but both numerator and denominator are time units. The value of B is 7/24, a "unitless" quantity. It is unitless because the time units (hour/hour) cancel, leaving no units.