X square plus 4x plus xy plus 4y?

In order to combine terms, the variable(s) must be the same and the exponent(s) must be the same on the variables. Since you have an x2 term, x term, xy term and y term, none of the terms can be combined. So, the answer is: x2 + 4x + xy + 4y. The only thing you could do in this problem is to factor out a 4 from the 4x & 4y so another way to write this is: x2 + xy + 4(x + y).