In 12 hours Bashar alone can complete the work.

In 4 hour, Ameen can do = 1 work

In 1 hour, Ameen can do =$\frac{1}{4}$ part

In 2 hours, Ameen and Cathy can do = 1 work

In 1 hour, Ameen and Cathy can do = $\frac{1}{2}$ part

In 1 hour, Cathy can do = ($\frac{1}{2}-\frac{1}{4}$) part

=$\frac{2-1}{4} = \frac{1}{4}$ part

Again, In 3 hours, Bashar and Cathy can do = 1 work

In 1 hour Bashar and Cathy can do = $\frac{1}{3}$ part

Bashar can do in 1 hour = ($\frac{1}{3}$ -$\frac{1}{4}$) part

= $\frac{4-3}{12}$ = $\frac{1}{12}$ part

$\frac{1}{12}$ part of work is done by Bashar in = 1 hour

1 part of work is done by Bashar in =$\frac{1×12}{1}$ = 12 hours.