In Exercises $67-70,$ the torque about the origin $O$ due to a force $\mathbf{F}$ acting on an object with position vector $\mathbf{r}$ is the vector quantity $\boldsymbol{\tau}=\mathbf{r} \times \mathbf{F}$. If several forces $\mathbf{F}_{j}$ act at positions $\mathbf{r}_{j},$ then the net torque (units: $N-m$ or $\left.l b-f t\right)$ is the sum $$ \boldsymbol{\tau}=\sum \mathbf{r}_{j} \times \mathbf{F}_{j} $$
Calculate the torque $\tau$ about $O$ acting at the point $P$ on the mechanical arm in Figure $21(\mathrm{~A})$, assuming that a 25 -newton force acts as indicated.