The weight of a circular disc varies directly as the product of the square of the radius and its thickness. Two identical/similar discs have their thickness in the ratio of 16: 9. What is the ratio of their radii if the weight of the first is four times that of the second?

Correct option is A

​$$\frac {W_1}{W_2} =\frac{ r_1^2 h_1}{r_2^2 h_2}\\\frac {4W_2}{W_2} =\frac{ r_1^2 \times 16}{r_2^2 \times 9}\\\frac {4 \times 9}{16} =\frac{ r_1^2 }{r_2^2} \\\frac{3}{2}= \frac{ r_1}{r_2}$$​​