Ed had 7 more marbles than Doug. Doug lost 18 of his marbles at the playground. If Ed had 35 marbles How many marbles does Doug have now?
Ed had 7 more marbles than Doug. 

That means that if we start with Doug's number of marbles, then add 7, we'll get Ed's number of marbles. 

Doug lost 18 of his marbles at the playground. 

That means that if we start with Doug's number of marbles, then subtract 18, we'll get Doug's current number of marbles. 

Ed had 35 marbles. 

That means that if we start with Ed's number of marbles, then subtract 35, we'll get Ed's current number of marbles. 

Now let's put it all together. If we start with Doug's number of marbles, then subtract 18, we'll get Doug's current number of marbles. And if we start with Ed's number of marbles, then subtract 35, we'll get Ed's current number of marbles. But we know that Ed's current number of marbles is 7 more than Doug's current number of marbles. So if we take Doug's current number of marbles, then add 7, we'll get Ed's current number of marbles. 

Therefore, Doug's current number of marbles is