GCSE Maths Practice: direct-proportion

\( \begin{array}{l}\text{Which of the following situations represent direct proportion?}\end{array} \)

Select all correct options:

\( \text{The cost of 3 pens is £3, and 6 pens cost £6.} \) \( \text{A car travels 60 miles in 2 hours and 90 miles in 3 hours.} \) \( \text{A worker is paid £50 for 5 hours and £60 for 6 hours.} \) \( \text{A jug holds 2 litres of water when full and 1.2 litres when half full.} \)