Timmy has x bushels of apples, he sells 10 bushels and then gets a shipment of 4y bushels of apples. Which expression represents the number of bushels Timmy now has?

The number of bushels is the sum of the bushels of the number of apples that he initially had, less the number of bushes of apples that he sold, plus the number of bushes that he received. This is x - 10 + 4y. In this case the number of bushels are represented in different ways, so you have to use algebraic signs.