Answer:
angle B'CA'= angle BCA..... (common angle)
angle B'A'C = angle BAC.....(corresponding angels)
therefore,
ΔCB'A' ~ ΔCBA. ......(by A-A test of similarity)
therefore,
B'A'/ BA. = CA'/ CA....(congruent sides of congruent triangles)
now, B'A' = 5, CA'= 6 , CA = 6 + 3 = 9
5 / BA. = 6 / 9
therefore, 5 / BA. = 2 / 3
[tex]ba \: = \frac{5 \times 3}{2 } \\ = \frac{15}{2} \\ = 7.5[/tex]
Answer : AB = 7.5 units