How can you generate x + 3y + 5 from the expression x + y + 4 + 2y + 1?

You need to combine like terms. If I regroup all the x's, y's and numbers together, it will result in the expression x + 3y + 5. 

(x) = x

(y) + (2y) = 3y

(4) + (1) = 5. 

Since they are all positive, you can add them and your final simplified answer is x + 3y + 5