Yan has four more apples than Xavier. If Xavier has x apples, use x, a number, and an operation to write anexpression for how many apples Yan has,

Xavier has "x" apples, and Yan has four more than him. The "more" implies an operation of addition. So in this case we can express the number of apple Yan has as:
[tex]\text{Yan}=x+4[/tex]