Question

45+y=100-15
13-a=21-12
12+c=90-70

Answer 1

45+у=100-15
у=85-45
у=40
45+40=100-15
84=85

13-а=21-12
13-9=а
4=а
13-4=21-12
9=9

12+с=90-70
с=20-12
с=8
12+8=90-70
20=20

Answer 2

у=100-15-45
У=40
-А=21-12-13
-а=-4
С=90-70-12
С=8