Answer:
(11√42)/2 
Explanation:
Thanks to the given information we can say that the smaller leg of the left triangle is 
(11√7)/2 
while the other leg is 
11/2 √7 * √3 = 11/2 √21 
the triangle on the right has two congruent legs. For the Pythagorean theorem 
x^2 = 2 (11/2 √21)^2 
x^2 = 2 * 121/4 * 21 
x^2 = 2541 / 2 
x = √11^2 * 3 * 7/√2 
x = 11√21/√2 
x = (11√42)/2