ssis - trying to derive a new column using a previous column? -

I have items, warehouse, and amounts but need to add and add two points of the new requirement item and the last warehouse This is what gives me the item + plant number. I am reading the flat file and removing these three columns but I am new to using an expression which will give me the last two digits of the warehouse and add 1. For example 513 warehouse, therefore the result would be 113. It will be really appreciated how far I have tried:

  items + 1 + SUBSTRING ("warehouse", 2,2)  

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