Deandra is doing her math homework. Out of 24 problems total, she completed the first 12 problems in 1 hour and the last 12 problems in 3 hours. What is the unit rate for all 24 problems?

Deandra completed 24 problems in total. Her total time was 1 + 3 = 4 hours, so the unit rate is 24 ÷ 4 = 6 problems per hour. The correct choice is 6 problems per hour.

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