On one day, a store sold 16 boxes of rice, restocked the shelf with 22 boxes, sold 27 boxes, restocked with 30 boxes, and sold 15 boxes. there are now 21 boxes of rice on the helf. how many boxes are on the shelf at the start of the day?

There are 27 boxes are on the shelf at the start of the day.

Step-by-step explanation:

Let number of boxes are on the shelf at the start of the day is x

According to given situations :

On one day, a store sold 16 boxes of rice

i.e,

Restocked the shelf with 22 boxes,

⇒

But 27 boxes sold

⇒  

Restocked with 30 boxes,

⇒  

But 15 boxes sold,

⇒  

There are now 21 boxes of rice on the shelf.  

So,  

Therefore,There are 27 boxes are on the shelf at the start of the day.

51

step-by-step explanation:

73-22=51 the   mass number minus the amount of protons gives you the amount of neutrons