A force of `-4Fhat(K)` acts O, the origin of the coordinate system. The torque about the point `(1,-1)` is

Explanation

Torque, `tau=rxxF=[(1-0)hat(i)+(-1-0)hat(j)+(0-0)hat(k)]xx(-10)hat(k)=10(hat(i)-hat(j))xx(-hat(k))=10(hat(i)+hat(j))Nm`