4)=-16,54-9,31-11,27+23,38=-(16,54+9,31+11,27)+23,38= -37,12+23,38=
= -(37,12-23,38)= -13,74
5) = 5 3/7-2 1/14+3 3/28=5 12/28 - 2 2/28 +3 3/28= 6 13/28
6) = 3 5/9 - 2 1/4+4 5/6 - 5 2/3= 3 20/36 -2 9/36+4 30/36 -5 24/36= (3 20/36+4 30/36) - (2 9/36+ 5 24/36) =7 50/36 - 7 33/36 = 17/36