а) 13 y+9 = 100
13 y-91 = 0
y = 7
б) 2 x-50 = 12
2 x-62 = 0
x = 31
в)
30-x = 60-3 x
2 x-30 = 0
x = 15
5y+(8y+9)=100
5y+8y+9=100
13y+9=100
13y=100-9
13y=91
y=91/13
y=7
x-(50-x)=12
x-50+x=12
2x-50=12
2x=50+12
2x=62
x=62/2
x=31
30-x=3(20-x)
30-x=60-3x
2x-30=0
2x=30
x=30/2
x=15
