ANS:B - 3.300 m

HI = RL + Staff reading on floor.
= 99.995 + 1.505 = 101.5m.

Here the staff was inverted against the roof and the staff reading is 1.795m.
So, HI + inverted staff reading.
= 101.5 + 1.795 = 103.295m.
So floor level = 103.295 - 99.995 = 3.3m. H.I of Instrument = 99.995+1.505 = 101.5 m.
As the second staff reading is negative this,
= 99.995-1.795= 98.2m.
= 101.5 - 98.2 = 3.3m answer. If the benchmark of a station 'A' is 100, Back sight is 1.4m, foresight is 1.5m then what will be the level of the line of sight? H.I = R.L+B.S.
= 99.995+1.505.
= 101.5.

The Floor Level Below The Slab = H.I+Inverted Staff Reading.
= 101.5+1.795.
= 3.30m. We can know, the distance between the floor and slab is always near around 3 m so answer we can predict options which are near about 3 m and second the technical specifications in the questions staff is held inverted so the b.s- f.s= 1.505-(-1.795 ) (- because staff is inverted) and answer is 3.3 m.