If T=number of 3-wheeled and one-saddled tricycles and B=the number of 2-wheeled and one-saddled bicycles, we have:
3T+2B=60 and T+B=24, so B=24-T. Substitute for B in the other equation:
3T+2(24-T)=60, 3T+48-2T=60, T+48=60, T=12 so B=12.
The number of tricycles is 12.