2.8x=20×4.2

x=30

Question 2: I really can't think of it.

Question 3:1+100 =101.

Powder: 4040 ÷ 10 1 = 40 (kg) Water: 4040 ÷10100 = 4000 (kg).

Question 4: Desk: 30× 3 = 90 yuan Chair: 30× 2 = 60 yuan.

I'm exhausted, please adopt!