Correct Answer - Option 3 : 1/30
Marcus's method of designing two-way slabs:
In Rankine's Grashoff method, the effect of restraint against the lifting of the corners and the effect of torsion in the slab were neglected.
Marcus has given an approximate method for determining BM in slabs, simply supported on four edges with corners prevented from being lifted and considering torsion in the slab.
In this method thickness of the slab is generally taken to be 1/30 of a shorter span.