\[\boxed{\mathbf{917\ (917)}\mathbf{.}\mathbf{\ }Еуроки\ - \ ДЗ\ без\ мороки}\]
\[\textbf{а)}\ a = 9;\ \ b = - 2,4:\]
\[a + b = 9 + ( - 2,4) = 9 - 2,4 = 6,6.\]
\[\textbf{б)}\ a = - 3\frac{1}{2};\ \ b = 1:\]
\[a + b = \left( - 3\frac{1}{2} \right) + 1 = 1 - 3\frac{1}{2} = - \left( 3\frac{1}{2} - 1 \right) = - 2\frac{1}{2}.\]
\[\textbf{в)}\ a = 4,5;\ \ b = - 1\frac{1}{2}:\]
\[a + b = 4,5 + \left( - 1\frac{1}{2} \right) = 4,5 - 1\frac{1}{2} = 4,5 - 1,5 = 3.\]
\[\textbf{г)}\ a = - 14,8;\ \ b = 14,8:\]
\[a + b = ( - 14,8) + 14,8 = 14,8 - 14,8 = 0.\]