If x varies directly to y and if x = 3, y = 5, then find the value of y when x = 7.8.

Correct option is B

Given:
x ∝ y
x₁ = 3, y₁ = 5
x₂ = 7.8
Formula Used:
x = ky
$$\frac xy$$​ = constant
Solution:
​$$\frac{3}{5}=\frac{7.8}{y} \\\ \\\Rightarrow y=\frac{7.8\times5}{3}\\\ \\\Rightarrow y=13\\\ \\$$​​