GCSE Maths Practice: direct-proportion

\( \begin{array}{l}\text{y is directly proportional to x.} \\ \text{When x = 4, y = 10. Find y when x = 9.}\end{array} \)

Choose one option:

\( \text{22.5} \) \( \text{21} \) \( \text{20} \) \( \text{18} \)