Answer
20 calls per hour
Work Step by Step
At 10 A.M., a total of 30 calls have been handled.
By 1 P.M., a total of 90 calls have been handled.
The increase in number of calls handled was:
$=90-30=60$
The elapsed time from 10 a.m. to 1 p.m. is 3 hours.
Thus, the average rate is:
$=\dfrac{60\text{ calls}}{3 \text{ hours}}=20$ calls per hour
