120 - y = 20 .
b + 25 = 100.
16 - a = 4 .
c - 3 = 13 .
15 + x = 30 .
60 - c = 50 .
17 - a = 9 .
b - 78 = 0 .
x + 70 = 100.
y - 8 = 15 .
100 - c = 60 .
b - 6 = 19.

120-у=20у=120-20у=100b+25=100b=100-25b=7516-a=4a=16-4a=12c-3=13c=13+3c=1615+x=30x=30-15x=1560-c=50c=60-50c=1017-a=9a=17-9a=8b-78=0b=78-0b=78x+70=100x=100-70x=30y-8=15y=15+8y=23100-c=60c=100-60c=40b-6=19b=19+6b=25