Answer
$5\ J$
Work Step by Step
Force ${\bf F}$ acting through a displacement ${\bf D}=\vec{PQ}$ does the work:
${\bf W}={\bf F}\cdot{\bf D}$
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${\bf F}=\langle 5\ N,0\ N\rangle,\qquad {\bf D}=\langle 1\ m,1\ m\rangle$
${\bf W}=(5N)(1m)+(0N)(1m)=5\ Nm=5\ J$
