解:(1)由题意,设y=k/(x-1.5),将(x,y)=(3,8)代入上式,得k=12所以,x与y之间的函数关系式为y=12/(x-1.5)(2)依题意,设当调至x元时,收益增加5%,有(1+5%)*10*(2.8-2.4)=y(x-2.4)化简得4.2=12(x-2.4)/(x-1.5)7(x-1.5)=20(x-2.4)7x-10.5=20x-4813x=37.5解得x≈2.9综上所述,当调至2.9元时,收益增加5%