A= 1/5/18+1/-7/12
B= 1/2-1/3-3*5/18+2-7/12
B = 3/6-1/6-15/18+24/12
B = 9/18 - 3/18 - 15/18 + 36/18
B = 9-3-15+36/18
B = 27