What size wire do I buy for my electrical service panel The NEC answers

250′ claflin 6-6 duplex aluminum urd direct burial cable 600v flat (2) jkt pump cable w/g. Feedback will be left as soon as feedback is left for us. Black sunlight resistant cross-linked polyethylene (XLP) insulation. Wire Gauge 6 AWG (4.1 mm). Neutral conductor has a yellow stripe.