3x + 5y = 48y = (48 - 3x)/5 = 9 + 3(1 - x)/5x = 1 ........小船y = 9 ........大船
小船x大船y3x+5y＝48x，y都是正整数x＝1，y＝9x＝6，y＝6x＝11，y＝3
