Auto-populate column based on another column

[technocrawl]

Hi there,

Actually I was trying to create an Excel document, whose primary purpose is Just Billing and printing. Everything that i made in it was working fine except few things.

All I want is, When I select the "Particulars" from the list, I want the "Unit Price" to be auto populated.

For example, If the "Particulars" is selected as "Shirt - 250", I want the "Unit price to be automatically filled with "250".
and one more thing thats really bugging me is, I want someone to help me generate the "Total Price" ( I11 Col ) by multiplying "Unit Price" with "Quantity", and i want this to be generated automatically when the "Quantity is filled by the user".

Everything is working fine before i hit the "New Invoice", then it moves away...

I even tried locking the cells containing the formulas, but still the same issue. I want all the transactions to be saved in the Sales sheet.

I am looking forward for Excel Geeks, who can fix this for me,...

Thanks in advance....