(2-1 5/18)+(7- 2 11/18)

36/18-23/18+6*18/18-2*11/18=13/18+4*7/18=92/18=5*1/9

(2-1 5/18)+(7- 2 11/18) = (2-23/18)+(7-47/18) = 36-23/18 + 126-47/18 = 13/18 + 79/18 = 92/18 = 46/9 = 5 1/9