She bought 30 more red apples than green apples. This is because they said that she bought four times as many red apples as green apples and times as many means to multiply. The total is 50 apples including both red and green. Lets say that there are 10 green apples so if you multiply 10*4 and add your result to 10 you should get 50. 10*4=40 and 40+10=50. Finally it asks you how many more red apples than green apples did she buy ( how many more is used to subtract ) so you subtract 40-10=30 so now you know that she bought 30 more red apples