a)
3(2-3x)=x-4
b)
x(x-4)=x(x+3)-49
c)
x-3(2-3x)=2(x-1)+x
6-9x=x-4
-10x=-10 / : (-10)
x=1
x^2-4x=x^2+3x-49
-7x=-49 / : (-7)
x=7
x-6+9x=2x-2+x
10x-3x=-2+6
7x=4
x=\frac{4}{7}