remember that you can do anything to an equation as long as you do it to both sides
also remember distributive property: a(b+c)=ab+ac
for that -(4-x)=-1(4-x)=(-1)(4)+(-1)(-x)=-4+x
so
-4+x=3/4(x-6)
multiply both sides by 4 to avoid distributing that fraction
-16+4x=3(x-6)
-16+4x=3(x)+3(-6)
-16+4x=3x-18
minus 3x both sides
-16+x=-18
add 16 both sides
x=-2