Let the second side be x
then,
first side = twice the length of the second side
= 2x
third side = 20 feet less than three times the second side
3 (second side ) - 20
= 3 (2x) -20
= 6x - 20
perimete of a triangle = sum of all sides,
substitute the values we know,
and you'll be left with this equation
106 = x + 2x + 6x - 20
106+ 20 = 9x
126 = 9x
126/9 = x
14 = x
so,
measure of second side = x = 14 feet
measure of first side = 2x = 2 (14) = 28 feet
measure of thurd side = 6x - 20 = 6 (14)-20 = 84- 20 = 64 feet.
