How do I solve this problem?

Answer:
x = 12
Step-by-step explanation:
(whole secant) x (external part) = (whole secant) x (external part)
(6+x) *6 = (4+23) * 4
(6+x) *6 = 27*4
6(6+x) = 108
Divide each side by 6
6+x =18
Subtract 6 from each side
6+x-6 =18-6
x = 12