Area = 54cm²
Height = 9m...
I want to believe you made a mistake in writing the unit for the height... Probably 9cm..
Comment if otherwise...
Area = 1/2 × base × height
54cm² = 1/2 × base × 9
Base = (54 × 2)/9
Base = 6×2
Base = 12cm....
Hope this helped...
