The condition is
30 < x <50 where x is an even number
You can write down numbers starting with 31 all the way to 49 on paper and try figuring it out from that.
OR
you can think of two numbers that is bigger than 30 and smaller than 50 where it's 2 digits add up to 6 and has to be even.
Can you think of any?
42
2+4 = 6
and 42 is an even number, so it meets all the requirements.