Write SQL query to solve given problem: What percentage of people named Mary who wants Receive Email promotions of AdventureWorks and selected partners are store contacts?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT CAST(SUM(CASE WHEN EmailPromotion = 2 THEN 1 ELSE 0 END) AS REAL) * 100 / SUM(CASE WHEN PersonType = 'SC' THEN 1 ELSE 0 END) FROM Person WHERE FirstName = 'Mary'