ANSWER
b = 2.9 m
Step-by-step explanation
The area of a triangle is,

Where b is the length of the base and h is the height of the triangle.
In this problem, we know that the area is A = 4.06 m² and the height is h = 2.8 m,

We have to solve this equation for b. Multiply both sides by 2,

And divide both sides by 2.8 m,

Hence, the length of the base is 2.9 m.