Find the torque of force 7i-3j-5k about the origin which acts on a particle whose position vector is 7i+j-k

Here, the torque can be found by calculating cross product of position vector and force.
T= R*F
Cross product can be calculated with the help of the following:
I*j = k
j*k = I
k*i = j
j*i= -k
k*j = -i
I*k = -j
and I*i, j*j, k*k = 0
so we have (7i + j - k) * (7i -3j-5k)
= -8i +28j-28k