How can I solve 4x+6y+5y+6y

That's not an equation, and it doesn't ask any question.  As it stands, there's nothing to "solve".

You may have been given an assignment to "simplify" it ... make it prettier and less complicated.

In order to do that, let's pretend for a moment that you're asked to add up a list that says:

                     4 chickens + 6 cows + 5 cows + 6 cows

I'm convinced that you would have no trouble at all adding up this list. You would
know right away that you can add up all the cows into one number, but you can't
add cows to chickens.  You would simplify the list,and it would become

                       4 chickens + 17 cows.

And now that you understand that, you're all ready to simplify the expression
in your question.  Just add up all the 'y's into a single number, but you can't
add 'y's to 'x's.

When you're done, you have 4x + 17y, and you're done.  That's all you can do with it.