Trained White horse writes math problems on chalkboard with mouth

Front:
/736 H.S.MAGUIRE TRAINER "MASCOTTE" EL. GRAN CABALIO. MATEMATICO "MASCOT" ADDING A FTER SUM

Back:
20 TRAEP TARJETA POSTAL PHILA ENGRAVING AND PHOTO COMPANY 112-14 N.NINTHST PHILADELPAIA PA. Lado que se reserva para la dirección