(12m-5m)x4=252 ; 28m=252;
m=252:28; m=9;////
4) (19n-6n):4=26; 13n=26*4;
n=104:13; n=8;///
2) (4n+3n)x11=154 ; 77n=154;
n=154:77; n=2;///
5) (16m+5m):18=7; 21m=18*7;
m=126:21; m=6;///
3)45:(4m-m)=3 ; 3m=45:3;
m=15:3; m=5;///
6) (17n-8n)x13=351;
9n*13=351;
9n=351:13;
n=27:9; n=3