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=20
у=120-20
у=100

b+25=100
b=100-25
b=75

16-a=4
a=16-4
a=12

c-3=13
c=13+3
c=16

15+x=30
x=30-15
x=15

60-c=50
c=60-50
c=10

17-a=9
a=17-9
a=8

b-78=0
b=78-0
b=78

x+70=100
x=100-70
x=30

y-8=15
y=15+8
y=23

100-c=60
c=100-60
c=40

b-6=19
b=19+6
b=25