Given:
XY = 8n + 4
YZ = 4n + 8
XZ = 15n - 9
Y between X and Z so, XY + YZ = XZ
So,
8n + 4 + 4n + 8 = 15 n - 9
solve to find n
So, combine like terms
12 n + 12 = 15 n - 9
12 n - 15 n = -9 - 12
-3 n = -21
divide both sides by -3
n = -21/-3 = 7
So,
The length of XZ = 15n - 9 = 15 * 7 - 9 = 96
