\(a) \, 5 + (-7) + 9 + (-11) +13 + (-15)\)
\( = \left[ {5 + \left( { - 7} \right)} \right]\)\( + \left[ {9 + \left( { - 11} \right)} \right]\)\( + \left[ {13 + \left( { - 15} \right)} \right]\)\(= ( -2) + ( -2) + ( -2) = -6\)
\(b)\,(-6) + 8 + (-10) +12 + (-14) \)\(+16\)
\( = \left[ {\left( { - 6} \right) + 8} \right]\)\( + \left[ {\left( { - 10} \right) + 12} \right]\)\( + \left[ {\left( { - 14} \right) + 16} \right]\) \(= 2 + 2 + 2 = 6\)
