We are given the equation:
[tex]{:\implies \quad \sf -2.1-\underline{?}=-1\dfrac12}[/tex]
Let assume the unknown value be x, so that:
[tex]{:\implies \quad \sf -2.1-x=-\dfrac32}[/tex]
[tex]{:\implies \quad \sf x-1.5=-2.1}[/tex]
[tex]{:\implies \quad \sf x=1.5-2.1=\boxed{\bf -0.6}}[/tex]
Hence, Option c) is correct
