How to calculate a result based on a data table

Hi, 

I have added a sample data file. On Sheet 2 is the 'master' data Clothing and Units. 

On sheet 1 I have produced what I need the final result to be. 

Basically Clothing will be a drop down. If Jeans are selected, Units will auto fill with '1'. When the sales amount is manually entered the Total Units will then be calculated. 

Can anyone help me with this solution please?