Question

300-m=200 66+b=900 525+a=702

Answer 1

300-m=200
m=300-200
m=100
-----------------
300-100=200
200=200

66+b=900
b=900-66
b=834
--------------------------
66+834=900
900=900

525+a=702
a=702-525
a=177
-----------------------
525+177=702
702=702

Answer 2

300-100=200,66+834=900,525+177=702. наверно так :-))