You’d have 2 tanks of fuel at point X, and need 1 left at the 8 parsec cache point, so you can spend one tank-- or 15 units-- going back and forth.
Ada 2 tanki penuh bahan bakar di titik X, dan selangkah lagi mencapai 8 parsec, sampai kamu dapat menghabiskan satu tanki atau 15 unit bolak balik.