The equation for the perimeter of a rectangle is:
2L+2W=P
Knowing this, we can plug in our values to determine P.
L = 9√11
W = 12√11
2(9√11)+2(12√11)=P
(18√11)+(24√11)=P
We can treat the square root of 11 as a variable and add the 18 and 24 giving us:
(42√11)=P
Your "exact" value is 42√11, if you're looking for your approximate value, it's 139.298241195.
Hope this helps.