There are two equattions here:
If all of it were ethene, 0.3 mol of hydrogen would be required. the extra 0.2 mol will saturate the extra bond in ethyne, so there must have been 0.2 mol of ethyne.
You can look at this another way:
0.3 mol will turn all the ethene into ethane, and all the ethyne into ethene. Then the other 0.2 mol will turn the remaining ethene into ethane (one to one).
Or you can do it the mathematical way, setting ethyne to
Then the amount of hydrogen needed is: