To find out whether Zane ate more pizza the first time or the second time, we just need to compare the fractions that he ate. An easy way to compare fractions when both fractions have 1 as the numerator (number on top of the fraction) is to think about a pie, and then think about that pie being split into a certain amount of pieces. If the pizza is split into 8 pieces, would the pieces be bigger or smaller than if the pizza was split into two pieces? Well, by logic we know that the more even pieces that you cut out of something, the smaller those pieces are going to have to get.
Therefore, 1/2 is bigger than 1/8, so Zane ate more pizza on his second time.
Hope that helped! =)