what is the missing sign between 3 and 2? I assume that it's multiplication sign, or *
3*2=6 (twice three is 6, because 3+3=6)
so the result of 3*2x is 6x, because 2x is actually 2*x, so we have 3*2*x - we are allowed to simplify this!
and 6 is the coefficient: the number by which a variable is multiplied.