Answer:
Height = 25.46 inches
Width = 50.92 inches
Explanation:
We can say area of a triangle is :
Area = 1/2 * length * height
The banner is twice as long and height, we can say:
length = 2*height
Since, area given as 648, we can write:

Height = 25.46 inches
Width = 2 * 25.46 = 50.92 inches