Plzzzzzz tell me this question plzzzz

Dear Student,
A can do a piece of work in 6 hours & B can do in 4 hours.

A’s 1 hour work =$\frac{1}{6}$
B’s 1 hour work = $\frac{1}{4}$
Both (A+B)’s 1 hour work = $\frac{1}{6}+\frac{1}{4}=\frac{5}{12}$$=\frac{2+3}{12}=\frac{5}{12}$
Both (A+B)’s 1 hour work $=\frac{5}{12}$

After the first has worked for 2 hours ' he is joined by the other,

(A)’s 2 hour work = $2\times \frac{1}{6}=\frac{2}{6}=\frac{1}{3}$
Remaining work $=1-\frac{1}{3}=\frac{3-1}{3}=\frac{2}{3}$
$\frac{5}{12}$work is done by (A+B) in 1 hrs
$\frac{2}{3}$ work is done by (A+B) in $\frac{12}{5}\times \frac{2}{3}=\frac{8}{5}$ hrs
Total time taken to be completed the work =$2+\frac{8}{5}=\frac{18}{5}=3\frac{3}{5}$hrs = 3hr 36 min

Regards