Question 372490
Two sides of an equilateral triangle have lengths 3x+1 and -2x+26. Which of 21-x or 3x-4 could be the length of the third side

3x+1 = -2x+26
  5x = 25
   x = 5

Lenght of any side = 3x+1 = 3(5)+1 = 16

(21-x) is the length of 3rd side