HELP ME PLEASE. THIS IS MY LAST QUESTION THEN I CAN GO TO BED.

Answer:
100.
Step-by-step explanation:
The 2 smaller triangles are similar, so:
48 / (x - 64) = 64 / 48
64(x - 64) = 48^2
x - 64 = 48^2/64
x = 48^2/64 + 64
= 100.