Answer: 6 problems per hour
Explanation:
The first hour, she completed 12 problems, but for the last 12 it took her 3 hours.
Time Space 1: 1 hour for the first 12.
Time Space 2: 3 hours for the last 12.
Since we already know that there are 24 problems total, and 12 plus 12 equals 24; we can add the hours together ( 1 + 3 = 4 )
24 problems took 4 hours to complete.
Divide the 24 problems by the 4 hours to get the basic unit of
6 problems per hour which is the answer