How do I Factor 5x+15+xy+3y

I saw right away that 5 is common to the left 2 terms and that y is common to the right 2 terms. Thus, 5 (x+3) + y (x+3) = (x+3) (5+y)

you split the problem into two separate problems and go from there.

so, (5x+15) and (xy+3y) then you take out the common factor in both

so, positive 5 out of (5x+15) and positive y out of (xy+3y)

you'll then have 5 (x+3) and y (x+3)

The x=3 is similar in both problems so you can combine them to make one and combine the two factors you took out to make another problem.

So your final answer is (x+3) (5+y)