.
    x + 2x + (x+24) = 84.
    4x + 24 = 84
    4x      = 84 - 24
    4x      = 60
     x       = 60/4 = 15.
The sides should be  15, 30 and 39 units.    ANSWER
CHECK.  The found side lengths satisfy the triangle inequalities --- hence, such a triangle does exist.
ANSWER.  The triangle side lengths, obtained from the condition, are 15, 30 and 39 units.
Solved, explained and checked.