4/7*(-3/4n)*7/9=-3/7n*7/9=-1/3n
#2
2(5x-4y)-3(4x-y)=10x-8y-12x+3y=-2x-5y
x=-5
y=0,8
-2*(-5)-5*0,8=10-4=6
#3
2k-(3k-8r)=2k-3k+8r=-k+8r
k+4r=17
-k=-8r:(-1)
k=8r
8r+4r=17
12r=17:12
r=1 5/12
k+4*1 5/12=17
k=17-17/3
k=17-5 2/3
k=11 1/3
-11 1/3+8*17/12=-11 1/3+34/3=-11 1/3+11 1/3=0
#4
-7/12x+2/3x-1/4x=-7/12x+8/12x-3/12x=-1/6x