The area of a rectangle is $99 cm²$. If the breadth of the rectangle is $9 cm$, find its perimeter. 

We are given a rectangle of area,  $99 cm²$ and breadth as $9 cm$.

For finding the length, we use the expression for calculating the area of rectangle which is:

$Area=length\times breadth$

Substituting the known values, we get:

$99=length\times 9$

simplifying which we get:

$length=11cm$

Now, we will use this length in finding the perimeter by the expression:

$P=2(length+breadth)$

Substituting the values, we get:

$P=2(11+9)$

$P=2\left(20\right)cm$

or we can say:

$P=40 cm$

Thus, the required perimeter of the rectangle is found to be: option (D) $40 cm$.