At 10 am the temperature was 71°f 3 pm the temperature was 86°f find the value of the slope and explain what it means

If you draw a graph of the temperature, you know two points
on the graph, (so naturally your graph is a straight line).

The two points are: 

           x = 10 hrs after midnight,    y = 71°F
and
           x = 15 hrs after midnight,    y = 86°F

Whenever you have two points on a graph, the slope
of the line between them is 

                   (y₂ - y₁) / (x₂ - x₁) .

Slope =  (86° - 71°) / (15 hrs - 10 hrs) =

                    (15°)   /   (5 hours)       =       3 degrees per hour .

What it means:

If the temperature was 71° at 10 AM and later it was 86° at 3 PM,
then from 10 AM until 3 PM the temperature increased at the
average rate of 3° per hour.

Graph a should be your answer