Dax for : Sum + a fixed value ( if a specific criteria is met ) , Otherwise just sum

[Jmens]

Hi All , 

   I am trying to create a measure that adds an absolute value ( which is not in the data model )  when a specific criteria is met .  For example in the table below i want to create a  Sales Forecast measure that adds £100 to the sales if the customer is "B" . 

    The +£100 will have to be manually typed in the measure .  Is this possible ? 🙂 

Customer	Sales	Absolute Value (Not in Data model )	Sales Forecast
A	10		10
B	15	100	115
C	20		20
Sum	45		145

   Any help will be much appreciated !

[Jmens]

 A better picture of the example 🙂