Alex bought twice as many pears as apples. He bought 4 more pears than oranges. He bought 6 apples.

How many oranges did Alex buy?

He bought twice as many pears as apples. We can say this as he bought 2 times more pears than Apples. Now that can be said as 2 times # of apples = # of pears. He also bought 4 more pears than oranges. So he bought #of oranges + 4=#of pears. If he bought 6 apples he bought 2*6 pears and so he bought 12 pears. Now since he bought 4 more pears than oranges then all we do is the opposite which is 12-4=oranges.

He bought 6 apples, 8 oranges, and 12 pears.

Alex bought 8 oranges. Since he bought six apples and he bought twice as many pears as apples, he bought 12 pears. since he bought 4 more pears than oranges, you subtract 4 from 12, which gives you 8.