Answer:
=if(Or(type = "Extra Large";type = "XX Large";type = "XXX Large");0;shipping cost)
Explanation:
While I cannot do exact reference to your excel shet I can tell you how to build the formula
you will use and if function to determinate wether the request fullfil or not the condition.
As there are several condition we use the Or function.
the "type" will be the cell on which you can reference the order side of a particular sale
Then, we write zero if positive (fulfil the criteria to get free shipping)
Then, you write the shipping cost. which is a number value
for example
1 2 3 4 5
A size extra large =if(Or(A2= "Extra Large";A2= "XX Large";A2= "XXX Large");0;shipping cost)