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23)

25 x + 30y = 2460 ---- (1)

1.1 (25x) + 0.95 (30y) = 2562 ---- (2)

(1) x 1.1

1.1 (25x) + 1.1 (30y) = 2706 ---- (3)

(3) - (2)

0.15 (30y) = 144 -----> y = 32

x = 60

ชนิดแรกแพงกว่า 60 - 32 = 28 บาท