Q$.3($a$)$ Briefly explain the rules of variation for the Engineer's Instruction Nos. $1,2,3$ and $4.$

Engineer's Instruction No$.1$

The depths of reinforced concrete beams in all typical floors are increased from $500mm$ to $750mm.$

Engineer's Instruction No$.2$

All timber framed doors are replaced with steel metal doors.

Engineer's Instruction No$.3$

Add accelerator to the reinforced concrete grade $\frac{30}{20}$ in external walls.

Engineer's Instruction No$.4$

Remove the existing $100mm$ diameter drain pipe due to relocation of drainage route.