\(a)\) \(\left( { - 23} \right).\left( { - 3} \right).\left( { + 4} \right).\left( { - 7} \right) \)
\(=\left[ {\left( { - 23} \right).\left( { - 3} \right)} \right].\left[ {\left( { + 4} \right).\left( { - 7} \right)} \right]\)
\(=69.\left( { - 28} \right) = - 1932\)
\(b)\) \(2.8.\left( { - 14} \right).\left( { - 3} \right) \)
\(=\left( {2.8} \right).\left[ {\left( { - 14} \right).\left( { - 3} \right)} \right] \)
\(=16.42 = 672\)