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a)

$\overline{u}=2\overline{\text{i}}-\overline{\text{j}}+2\overline{\text{k}}$
$\left|\overline{u}\right|=\sqrt{2^2+\left(-1\right)^2+2^2}=\sqrt{9}=3$
$\overline{u}^0=\frac{\overline{u}}{\left|\overline{u}\right|}=\frac{2\overline{\text{i}}-\overline{\text{j}}+2\overline{\text{k}}}{3}=\frac{2}{3}\overline{\text{i}}-\frac{1}{3}\overline{\text{j}}+\frac{2}{3}\overline{\text{k}}$
b)

$\overline{v}=-15\overline{u}^0=-10\overline{\text{i}}+5\overline{\text{j}}-10\overline{\text{k}}$

c)
$\overline{OP}=\overline{OA}+\overline{v}=\overline{OA}+-15\overline{u}^0=-8\overline{\text{i}}+5\overline{\text{j}}-15\overline{\text{k}}$
$P=\left(-8{,}\ 5{,}\ -15\right)$