The running back's total yardage is 21 yards
From the question we are given the following parameters
Distance travelled in the first half of the game is 9 yards
Distance travelled in the second half of the game is 12 years
In order to determine the running back's total yardage, we will take the sum of the distance travelled as shown
Total distance travelled = 9 yards + 12 yards
Total distance travelled = 21 yards
Hence the running back's total yardage is 21 yards
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