We have,
the distance travelled to bring the first potato, a1 = 2 24 = 48 m,
the distance travelled to bring the second potato, a2 = 2 (24 + 4) = 56 m,
the distance travelled to bring the third potato, a3 = 2 (24 + 4 + 4) = 64 m,
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So, he would have to run 2480 m to bring back all the potatoes.