What is 2x plus 3y plus 4x plus 9y?

To simplify the expression 2x + 3y + 4x + 9y, you first combine like terms. Adding the coefficients of x terms gives 2x + 4x = 6x. Similarly, adding the coefficients of y terms gives 3y + 9y = 12y. Therefore, the simplified expression is 6x + 12y.