12
Step-by-step explanation:
based on pythagorean triples 5, 12, 13 and 8, 15, 17.
x= 20
set up a proportion:
(2x - 4)/24 = 39 / (x + 6)
(2x - 4)(x + 6) = 936
2x^2 + 8x - 24 = 936
x^2 + 4x - 12 = 468
x^2 + 4x - 480 = 0
(x - 20)(x + 24) = 0
x= 20, -24
has to be positive so x = 20