It's embarrassing that I can be thrown off by such a seemingly simple question, but I really cannot understand why one of my methods isn't working.

Question: Evaluate 9x^{2}y+3y^{4 }when x=4 and y=-2. When I do ((9*4-2)+(3*-2^{2})^{4}) I get -336 but the correct answer is -240.

When I use the graphic calculator and just store x as 4 and y as -2 it gives me the -240. Help?