DC generator speed?

Hi the question is: "a dc generator is produced using one pole pair having a square surface of 6cm x 6cm and produces a flux density of 18mWb. The commutator has 4 segments which allows for two simple loops to be connected, two brushes are used with the positive applied to the brush nearest the south pole passing a current of 15A. What speed will it need to be driven to give an O/P of 240v DC?"







F= BIL







B= 13.89, I= 15A, and L = 0.06m