How to Add some values in column A based on related values in the same row in column B?

I am a teacher trying to use a formula to add sporting points earned by students if they are in a particular sporting house. The sporting House Column 'B' contains values B or R. The Points earned column contain numbers only.

How do I add all the points earned by students if their House value is B?

I tried the following embedded IF SUM formula:

IF(B2:B11)='B',SUM(L2:L11) but it did not work.

I would like to do this so that any new students entered and given a house will automatically be included in the total point scoring for that sporting house.

Please help.