From section A6.9, the torque of this multi-cell member can be related to
the shear flows in exterior walls as follows
For elastic continuity, the angles of twist in all cells must be equal
The direction of twist chosen to be positive is clockwise.
NOTE: Since the exterior walls in each cell have equal shear flows, we can factor the shear flow out and multiply it by the sum of the quotient S/t of the exterior walls.
The above equations for angle of twist together with the torque equation provide a total of 4 linear equations which can be solved simultaneously for the 3 unknown shear flows (i.e., q1, q2, and q3) and 1 unkown angle of twist.