If x : y = 3 : 4, then (7x + 3y) : (7x - 3y) is equal to?

Answer: Option C

$$\begin{array}{rl}& x:y=3:4\\ & \frac{\left(7x+3y\right)}{\left(7x-3y\right)}\\ & =\frac{y}{y}\left(\frac{7\frac{x}{y}+3}{7\frac{x}{y}-3}\right)\\ & =\frac{7\times \frac{3}{4}+3}{7\times \frac{3}{4}-3}\\ & =\frac{\frac{21}{4}+3}{\frac{21}{4}-3}\\ & =\frac{\frac{21+12}{4}}{\frac{21-12}{4}}\\ & =\frac{11}{3}or11:3\end{array}$$