请教gwd 一道数学题

1.material A cost $3/kilogram,material B costs $ 5/kilogram ,If 10 kilograms of material K consists of x kilograms of material A and y kilograms of material B ,is x> y ?

(1)y > 4

(2)the cost of the 10 kilograms of material k is less than $ 40

key：B 但我觉得 B 没办法判断啊  请教NN

x+y=10

3x+5y《40

可以求出