Solution:-

From the figure it is given that, AB, EF and CD are parallel lines.

(i) Consider the ∆EFG and ∆CGD

∠EGF = ∠CGD [Because vertically opposite angles are equal]

∠FEG = ∠GCD [alternate angles are equal]

Therefore, ∆EFG ~ ∆CGD

Then, EG/GC = EF/CD

5/10 = EF/18

EF = (5 × 18)/10

Therefore, EF = 9 cm

(ii) Now, consider the ∆ABC and ∆EFC

EF ||AB

So, ∆ABC ~ ∆EFC

Then, AC/EC = AB/EF

AC/(5 + 10) = 15/9

AC/15 = 15/9

AC = (15 × 15)/9

Therefore, AC = 25 cm