Soo, a monomial is basically a polynomial that only has one term. So, in this case, the polynomial -6am is totally a monomial because it only has that one term. Ah-mazing, right?
Let's break it down even further. To figure out if a polynomial is a monomial, we gotta look at the leading coefficient (it's just the number in front of the term with the highest degree) and the number of terms. In this case, the leading coefficient is -6 and the number of terms is only one (which is -6am). So, BOOM, it's a monomial!
Just to make it crystal clear, -6am is like the perf example of a monomial because it only has that one term with the leading coefficient of -6.
Hope that helps you out! ; )