Answer : 19
First, let our 19 be x
11+(19+6)=(11+ x)+6.
Then,
(11+x)+6=11+(19+6)
Now,
(11+x)+6: x+ 12.
Refined..
Remove parenthesis.(11+6x)+6 = 11 + x +6
Now, group like terms.
x+6+11
Add the numbers
=x + 17
Refined..
11+(19+6) : 36
x+ 17=36
Subtract 17 from both sides.
x+17-17=36-17
x= 19.
Hope this helps. :)