Answer: the length of the base of the banner is 3 meters.
Explanation:
Assuming the banner is in the shape of a right angle triangle, we would apply the formula for determining the area of a triangle which is expressed as
Area = 1/2 × base × height
Let b represent the base
The banner is in the shape of a triangle with a height that is 4 times as tall as the base length of the banner. It means that the height of the banner is 4b
If the total area of the banner is 18 square meters, it means that
18 = 1/2 × b × 4b
18 = 2b²
b² = 18/2 = 9
b = √9 = 3 meters