Help writing sql for Linnworks

Hello I use a software called linnworks which uses SQL to export data. I so far have the following script:

SELECT
sc.ChannelSKU
,si.PurchasePrice
,si.ItemNumber
FROM Stock_ChannelSKU sc
LEFT JOIN StockItem si ON si.pkStockItemId = sc.fkStockItemId
GROUP BY
sc.ChannelSKU
,si.PurchasePrice
,si.ItemNumber


The database structure is shown here:
https://www.linnworks.com/assets/6c73379f21/pOtIaEgrzlSYxSQxcPgF3Hx8iYeMfwZbkw.png


Currently this outputs:

ChannelSKU
PurchasePrice
ItemNumber

I want to modify this script to show:
ChannelSKU
Price1 - This is formula 1 below
Price2 - This is formula 1 below
ItemNumber


Formula 1: ("si.PurchasePrice"+3.00)*1.2
Formula 2: ("si.PurchasePrice"+3.00)*1.3

Effectively taking the Purchase Price adding 3 and then after multiplying the whole number by 1.2

Linnworks creates the export file if I put in the correct information.

Also if its possible to find out how to add the channel name that would be ideal as well.