Given: The side of the square park = 60 m

The length of the rectangular park = 90 m

According to the question,

Area of square park = Area of rectangular park

⇒ side x side = length x breadth

⇒ 60 x 60 = 90 x breadth

⇒ breadth = (60 x 60)/90 = 40 m

Thus, the breadth of the rectangular park is 40 m.