IFs & AND formulae

Can you please tell me how I group the following:

=IF(AND(B3>=100,B3<=150),"15",""),(B3>=150,B3<=200),20",""),(B3>=200,B3<=250),25",""),(B3>=250,B3<=300),30","")) The formulae will eventually look like this: If (B3 = 100 to 150 then put 15 B3 = 150 to 200 then put 20 B3 = 200 to 250 then put 25 B3 = 250 to 300 then put 30 else leave blank) Thanx for your help