40 cm.
let the length of the first part be 3x, second part be 4x, third part be 5x.
where x is a positive length in cm.
why 3x,4x and 5x ?
so that the ratio of lengths of the 3 parts be 3:4:5.
total length of the stick = 3x + 4x + 5x = 12x=96cm
so x=96/12 = 8cm
therefore the largest part of the stick (5x)= 5*8 =40cm
