a)
$\left | 4 + 5 \right | = \left | 9 \right | = 9$
$\left | 4 \right | + \left | 5 \right | = 4 + 5 = 9$
$\Rightarrow \left | 4 + 5 \right | = \left | 4 \right | + \left | 5 \right |$
b)
$\left | (-4) + (-5) \right | = \left | -9 \right | = 9$
$\left | -4 \right | + \left | -5 \right | = 4 + 5 = 9$
$\Rightarrow \left | (-4) + (-5) \right | = \left | -4 \right | + \left | -5 \right |$