Answer:
see explanation
Step-by-step explanation:
Calculate the slope m using the slope formula
m = (y₂ - y₁ ) / (x₂ - x₁ )
with (x₁, y₁ ) = (2, 5) and (x₂, y₂ ) = (4, 10) ← 2 points on the graph
m =
= 
This means that 5 mm of rain falls every 2 hours