\[28 - c^{2}\]
\[c = 12:\]
\[28 - 12^{2} = 28 - 144 = - 116.\]
\[c = 0:\]
\[28 - 0^{2} = 28 - 0 = 28.\]
\[c = - 1:\]
\[28 - ( - 10)^{2} = 28 - 10^{2} =\]
\[= 28 - 100 = - 72.\]