+2669 The function f(x) is defined for 1 \le x \le 5 as follows:
-2x + 4 & \text{if }1 \le x \le 2, \\
5 - x & \text{if }2 < x \le 3, \\
9 - 2x & \text{if }3 < x \le 4, \\
6 - x & \text{if }4 < x \le 5.
Find all real numbers x such that f(x) = 18.
