2/9*1,8m-2/9*5,4-3/7*2,1m+3/7*4,2=

2/9(1,8m-5,4)-3/7(2,1m-4,2)=2/9(1  8/10m- 5 4/10)-3/7(2  1/10m-  4  2/10)=

=(2/9* 18/10m-2/9*54/10)-(3/7*21/10m-3/7* 42/10)=(36/90m-108/90)-(63/70m-126/70)=

=(4/10m-6/5)-(9/10m-9/5)=4/10m-6/5-9/10m+9/5=-5/10m+3/5=-1/2m+3/5 дамю так