two sides are 3 and 6
since triangle is isosceles , the third side can be either 3 or 6
In a triangle , sum of two sides > third side
checking for third side=3 we have {3,3,6}
3+3>6, 6>6 ( false)
checking for third side =6 , we have (3,6,6)
3+6>6 , 9>6 ( true)
6+6>3, 12>3 (true)
so the third side must be 6
Option C. 6 is the correct answer