what is the possible third side ?

Question

8 ft & 12ft are the two other sides so what is the length of third side

Answer 1

Its length must be less than the sum of the lengths of the other 2 sides, so it must be less than 8+12 = 20.  But it must also be larger then the difference of the other 2 sides, so it must be larger than 12-8=4. That puts the length between 4 and 20.