From Mechanics

\displaystyle \begin{align} & \mathbf{F}1 = & 86\textrm{.}6\mathbf{i}+50\mathbf{j}\ \text{N}\\ \end{align}

\displaystyle \begin{align} & \mathbf{F}2= & -30\textrm{.}8\mathbf{i}+84\textrm{.}6\mathbf{j} \ \text{N}\\ \end{align}

\displaystyle \begin{align} & \mathbf{F}3= & -80\mathbf{j}\ \text{N}\\ \end{align}

Summing these vectors give their resultant

\displaystyle \begin{align} & \mathbf{R}= & 55\textrm{.}8\mathbf{i}+54\textrm{.}6\mathbf{j} \ \text{N}\\ \end{align}

The magnitude of this resultant is

\displaystyle \sqrt{{{\left( 55\textrm{.}8 \right)}^{2}}+{{\left( 54\textrm{.}6 \right)}^{2}}}=78\textrm{.}1\ \text{N}