Answer:
1.50 h
Step-by-step explanation:
For an object moving in uniform motion (= moving at cosntant velocity), the relationship between speed, distance and time is given by:

where:
v is the speed of the object
d is the distance covered
t is the time taken to cover the distance
For this problem, we have:
d = 18 miles is the distance covered by David
is David's speed
Therefore by re-arranging the equation, we can find the time taken by David to cover that distance:
