Make cells only able to insert amount of specific cell and its multiple value

[TheLSD]

Hi guys,
is there any way to make some specific cells to only able insert a specific amount and the multiple of it?
also, is there any way to make a cell count by the value of the data and the multiple of it?
let's say that from the table below, I type price per amount 10,000, then the user is only able to add 10,000 too or the multiple (20,000 or 30,000 or else)
and then for the Quantity, when the user already type which month, it counts from the value of the cell depending on the price per amount, for example, if I type 10,000 on Jan, 20,000 on Feb, 0 on March, and 10,000 on Apr, the Quantity column shows 4.

any suggestion is much appreciated, thanks!!

Quantity	Price per amount	Jan	Feb	Mar	Apr
4	10,000	10,000	20,000	0	10,000

 

[TheLSD]

Forgot to add,
If the Price Per Amount is empty, then the user can freely add the amount on Month columns and the Quantity column remain empty