Right option is (c) ndt – n’p^2t/4g
The explanation is: The net area of flat with staggered hole is given by : A = (b – ndh + n’p^2/4g)t, where b = width of plate, n = number of holes in zig-zag line, n’ = number of staggered pitches, p = pitch distance, g= gauge distance, t = thickness of flat.