The ratio is 1/1.5 so just pick the answers where the first number multiplied by 1.5 is equal to the second number.
For example the first option says 2 and 3.
2 times 1.5 is equal 3 so that is one of the answers.
If an option says 4 and 5, 4 times 1.5 is 6 not 5 so that wouldn't be an answer.