When it says you need self raising flour for date cake how much baking powder is required to make plain into raising?

Self-raising flour has a raising agent (typically baking powder) already added to the flour. For every cup of plain all-purpose flour, you need to add 1 1/2 teaspoons of baking powder to make self-raising flour.

1 cup plain all-purpose flour = 1 cup + 1 1/2 teaspoons baking powder = self-raising flour