Answer:
6 problems per hour
Explanation:
Total problems = 24
she completed the first 12 problems in 1 hour
The last 12 in 3 hours.
Total time = 1 hour + 3 hours
= 4 hours
unit rate for all 24 problems = total number of problems / total time taken
= 24 problems / 4 hours
= 6 problems per hour