(13цел-8цел9/10)+(26цел1/2-15цел1//5-7)+(3цел3/10+8цел1/2)=

(13 - 8 9/10) + (26 1/2 - 15 1/5) - (14 1/5 - 7) + (3 3/10 + 8 1/2) = 4 1/10 + (53/2 - 76/5) - 7 1/5 + (33/10 + 17/2) = 41/10 + (265-152)/10 - 36/5 + (33+85)/10 = 41/10 + 113/10 - 36/5 + 118/10 = (41+113-72+118)/10 = 200/10 = 20