Answer:
0
Step-by-step explanation:
Apparently, you want the value of ...
[tex]\dfrac{1}{3}m-1-\dfrac{1}{2}n = \dfrac{m}{3}-\dfrac{n}{2}-1\\\\=\dfrac{21}{3}-\dfrac{12}{2}-1=7-6-1\\\\=\boxed{0}[/tex]
The value of the given expression for the given variable values is zero.