One bricklayer can build a wall in 6 hours. another bricklayer could build the same wall in 4 hours. if they work together, how long will it take to build the wall?

Hello,

Let's
V1 the velocity of the 1st bricklayer,
V2 the velocity of the 2nd bricklayer,

1wall=V1*6==>V1=w/6
1wall=V2*4==>V2=w/4
==>V1+V2=w/6+w/4=10w*24=5w/12

Let's t the time for the 2 bricklayer to build the wall
(V1+V2)t=w
==>5w/12*t=w
==>t=12/5 (h)=2h24min.

The answer is