Element X is vanadium. Here's how we know...
Start by assuming we have 100 g of this compound. That way, the percentages translate directly into masses: 44 g of O and 56 g of X.
Now, calculate the moles of oxygen:
Now, since the formula is
Since there is actually 2.75 moles of O, there must be #2.75 xx 2/5 = 1.1 moles of X.
Since 1.1 mole of X has a mass of 56 g, the molar mass of X must be
Looking at the periodic table, we see it must be vanadium.