If x : y = 7 : 3, then the value of xy + y^2x^2 - y^2 is

Answer: Option A

$$\begin{array}{rl}& =\frac{x}{y}=\frac{7}{3}\\ & =\frac{xy+y^2}{x^2-y^2}\\ & =\frac{\left(\frac{x}{y}\right)+1}{\left(\frac{x^2}{y^2}\right)-1}\\ & =\frac{\frac{7}{3}+1}{{\left(\frac{7}{3}\right)}^2-1}\\ & =\frac{10}{3}\times \frac{9}{40}\\ & =\frac{3}{4}\end{array}$$