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
$$\Rightarrow$$ side$$\times$$side$$=$$length$$\times$$breadth
$$\Rightarrow 60\times 60=90\times$$breadth
$$\Rightarrow$$ breadth$$=\dfrac{60\times 60}{90}=40$$m
Thus, the breadth of the rectangular park is $$40$$m.