Holding price calculation and selling stock

Hello Team,

I have a clarificaiton regarding the holding avg price calculation. Would like to understand related to the partial selling when the stock price is falling. Checked in internet that FIFO is been used, when trying to sell stock, so would like to understand it with example

Buy 10 @ 100
Buy 10 @ 90
Buy 10 @ 80

based on the above, the holding price is calculated as
(100*10 + 90*10 + 80*10 ) / ( 10 + 10 + 10 ) = 90

holding avg price = 90
holding qty = 30


now if the current price is 95 and if i sell as below

Sell 10 @ 95

below are the clarifications

Q: when 10 qty its sold, does it get calcualted like below,

= ( sell price - holding avg price ) * 10
= ( 95 - 90 ) * 10
= 50

in this case i am getting profit of 50


Q: or does it get caluclated using FIFO method

= ( sell price - last old trade price ) * 10
= ( 95 - 100 ) * 10
= -50

in this case I am incurring a loss of -50


Pls help me understand