For a free body diagram shown in the figure, the four forces are...

Let additional force required be $\overset{\to}{F}$.

Vector sum of the four forces and additional force.

\overset{\to}{F} + 5\overset{^}{i} - 6\overset{^}{i} + 7\overset{^}{j} - 8\overset{^}{j} = 0

Force required to make net acceleration zero

\overset{\to}{F} = \overset{^}{i} + \overset{^}{j}

Therefore, the required force is \left|\overset{\to}{F}\right| = \sqrt{{1}^{2} + {1}^{2}} = \sqrt{2}N$</p><p>Angle with$x$-axis:$tan\theta = \dfrac{ycomponent}{xcomponent} = \dfrac{1}{1}$</p><p>Thus,$\theta = 45 °