To find the slope, we use the formula for slope,

Letting the point (2,5) be
and the point (4,10) be
.
Now plugging in these values in the formula for slope, we get,
. The slope is
.
This basically means 5 mm of rain falls in every 2 hours, or 2.5 mm of rain falls every hour (
)
ANSWER: Slope is
and 5 mm of rain falls every 2 hours.