To solve this problem we must apply rule of three.
The first time we have to obtain the area in acres:
1 ha --------- 2.5 ac
121.2 ha --------- y
So we have:
1 ha . y = 121.2 ha . 2.5 ac
y = 121.2 ha . 2.5 ac / 1 ha
y = 303 ac
Answer: the area of countryside burned by wildfire was 303 acres.