ANSWER
20
EXPLANATION
We have the proportion given.
One way of solving this is writing:
4 deliveries = 2 hours
x deliveries = 10 hours
where x is the missing number
Then, cross-multiply:
4 * 10 = x * 2
=> 40 = 2x
Divide through by 2:
x = 40 / 2
x = 20
The missing number is 20.
