1. (9 + а) +11=20+а;
2. (16 + b) + 4=20+b;
3. (a +17) + 23=a+40;
4. (b +22) + 18=40+b;
5. (18 + х) + 12=30+x;
6) (43 + y) + 57=100+у.
1. (9 + а) +11=20+а;
2. (16 + b) + 4=20+b;
3. (a +17) + 23=a+40;
4. (b +22) + 18=40+b;
5. (18 + х) + 12=30+x;
6) (43 + y) + 57=100+у.