When using the tray balance to hold medicine, the medicine should be placed on the side of _ _ _ _ _ _ _ _ _, and the position of the marching code when reaching balance is as shown in the figure, and the weight is 20g, then the medicine.
When weighing drugs with a tray balance, the drugs should be placed on the left plate of the balance;
From the picture, the weight is 20g, and the scale indicated by the boarding code is 2.4g 。
∴ The mass of the tested drug is 20g+2.4g = 22.4g 。
So the answer is: left; ? 22.4.