the area of a rectangle is the multiplication of its width times its length, that is:
area = width*length
We have to write as an equation the information about the relationship between the width and the length, they say the width is 1/4 of the lenght, this is:
width = lenght/4
now we substitute the data we have:
area = width*length
144 = (length/4)*length
length^2 = 4*144 = 576
the length is raised to the second power because we had to multiply length*length, so to solve the last equation we had to take the square root to both sides:
length = √576
length = 24
so the length of the banner is 24 feet, and we know that:
width = lenght/4
width = 24/4
width = 6
so the width is 6 feet