A crepe store sells chocolate and peanut butter crepes. A chocolate crepe requires 3 units of chocolate spread and 6 units of crepe mix. A peanut butter crepe requires 4 units of peanut butter spread and 7 units of crepe mix. Recently, the peanut butter crepe has been more popular and therefore the number of peanut butter crepes made must exceed the number of chocolate crepes made. However at least 25% of the crepes made should be chocolate. The store has available 400 units of chocolate spread and 450 units of peanut butter spread. How many of each should the store make to minimize the total amount of crepe mix needed?