48.4%
For this problem, you don't even need to look up the atomic weights. Just simply determine how many percent of 7.28 is 3.52? So do the division.
3.52 / 7.28 = 0.483516484 = 48.3516484%
And of course, round the result to 3 significant figures since that's how many significant figures we have in our data, so we get 48.4%
