2 1/2*(2/15-3 5/6)+1/4
Вота..........................................
2/15-3 5/6=4/30-3 25/30=-3 21/30=-3 7/10
2 1/2*(-3 7/10)=5/2*(-37/10)=-37/4=-9 1/4
-9 1/4+1/4=-9