se vede doar jumatate de exercitiu
a. -6/108+5/90=-1/18+1/18=0 (am simplificat in diagonala)
c. 21/28-45/36=3/4-5/4=-2/4=-1/2=-0,5
e. (-3/8+15/8)·4/3=12/8·4/3=4/2=2
g. -9/2·(7/6-13/2)=-9/2·(7/6-39/6)=-9/2·(-32/6)=3/2·32/2=3·8=24
i. (19/6·5/19-16/7·21/48)·3/7=(5/6-16·3/48)·3/7=(5/6-1)·3/7=-1/6·3/7=-3/14
