7,(15)=(715-7)/99=708/99
2,(18)=(218-2)/99=216/99
5,(23)=(523-5)/99=518/99
11,(20)=(1120-11)/99=1109/99
7,(15)+2,(18) - 5,(23)+11,(20)=
=708/99+216/99-518/99+1109/99=1518/99=506/33=46/3=15,(3)
5,2(7)=(527-52)/90=475/90
6,1(3) =(613-61)/90=552/90
3,5(3) =(353-35)/90=318/90
2,2(2)=(222-22)/90=200/90
b) -5,2(7) + 6,1(3) - 3,5(3) + 2,2(2)=
=-475/90+552/90-318/90+200/90=
=-41/90=-0,4(5)
