Hey there!!
We know that there are two squares.
One thing we will need to keep in mind is that the measure of all the sides in a square are equal.
Ratio of square 'a' to square 'b' = 3:5
Given this, we don't know what the constant is, let's assume it as 'x'.
Hence, the ratio now is 3x:5x
With this, we will also know that the measure of the side of square 'a' is 3x and square 'b' is 5x.
It is given that, the perimeter of square 'b' is 60.
Perimeter = adding up all the sides.
As all sides are equal, the perimeter =
... 5x+5x+5x+5x=60
... 20x=60
... x=60/20
... x=3
Now we know that the constant is 3.
Now, let's find the measure of side of square 'a'.
3x = 3(3) = 9
Area = (side)²
... (9)²
... 81
Hence, the required answer is 81.
Hope my answer helps!