show step by step for better understanding

From the given floor plan, the following data are obtained:

$DL=5$kPa $($including its own weight$),LL=8$kPa,

Dimensions and stresses:

Beam $=250x400mm$; f$\text{'}$c $=24$MPa, Clear cover to slab $=20mm$; Slab reinforcement $=12mm$ bars; fy $=415$MPa

$S=3m($center to center$)L=6\mathrm{.}0($center to center$)$