This is the formula for area of triangle
1/2 × b × h = a
We know from the question:
a = 228 m²
h = 19 m
and the question what is the b?
Input the number to the formula
1/2 × b × h = a
1/2 × b × 19 = 228
b × 19 = 228 × 2/1
b × 19 = 456
b = 456/19
b = 24
The base is 24 m
