Answer: 10.9 cm
Step-by-step explanation:
The equation to find the area of a triangle is
Base x height x 1/2 = area
Since you are given the area, rearrange or “do the opposite” to find the base
(Area x 2 ) / height = base
30 x 2 = 60
60/ 5.5 = 10.9
Hope this helped :)