$\underset{\_}{\text{P}-\text{Q}=3}$

$2\text{P}=10$

$\text{P}=5\text{N}$

$\text{5}+\text{Q}=\text{7}$

$\text{Q}=\text{7}-\text{5}$                                           

$\text{Q}=\text{2}$

${\text{P}}_{\text{1}}=5+3=8\text{N}$

${\text{Q}}_1=3+2=5\text{N}$

$\theta =\text{60°}$

$\text{R}=\sqrt{{\text{P}}^2+{\text{Q}}^2+2\text{PQ}\cos \theta }$

$=\sqrt{64+25\times 2\times 40\times \frac{1}{2}}$

$=\sqrt{64+25+40}$

$=\sqrt{129}\text{N}$