Correct answer is the 3rd one.
108=2x-4(2x-9)
108=2x-8x+36
108=-6x+36
-36 -36
72=-6x
72/-6=-6x/-6
-12=x
one term is monomial
two terms are binomials
three terms are trinomials
each term is separated by a + or - sign
so......6 has only one term ......it is a monomial