Assume that the length of the rectangle is l and the width is w.
From the givens, we can conclude that:
l=9+w
Area of rectangle=l * w
90 = (l *w) = (9+w)(w)
90=9w+w^2
w^2+9w-90 = 0
either w=6
or w=-15 (this value is rejected as length cannot be negative)
therefore, the dimentions are as follows:
length=9+6=15 cm
width=6 cm
