1 watermelon =2 pineapples +6 apples

So the third pile =2 pineapples+14 apples.

Compared with the second pile, we can see that

1 pineapple =3 apples

So 1 weight of a pineapple: 150*3=450 (g)

So 1 weight of a watermelon: 2 * 450+6 *150 =1800 (g).

So the weight of each pile:1800+8 *150 = 2700 (g)