7020-m*3=4080
3m=7020-4080
3m=2940
m=2940:3
m=980
6k-2284=5456
6k=5456+2284
6k=7740
k=7740:6
k=1290
n:7+1275=6000
n:7=6000-1275
n:7=4725
n=4725*7
n=33075
2160:u+4996=5000
2160:u=5000-4996
2160:u=4
u=2160:4
u=540
1) (6,72:3/5+1,1/8*0,8) : 1,21-6,3/8=3,5/8