Ed had 6 more marbles than Doug. Doug lost 7 of his marbles at the playground. If Ed had 22 marbles how many marbles does Doug have now?
Ed had 6 more marbles than Doug. So if we start with Doug having 0 marbles, then Ed would have 6. 

Doug lost 7 of his marbles at the playground. So now Doug has 0 - 7 = -7 marbles, and Ed has 6 - 7 = -1 marbles. 

But we know that Ed has 22 marbles. So Ed has 22 - (-1) = 23 marbles. 

Therefore, Doug has 23 - 6 = 17 marbles.