If the slope of a regression line is positive, the correlation is positive.

 16y² - x²

Step-by-step explanation:  The - sign means a difference, so the choices with + signs are eliminated (though 64x² and 9 are squares)

10 is not a square so that one is eliminated (though the y² and the 4x² are squares)

16 is the square of 4, y² is the square of y, and x² is the square. That expression shows a difference of squares.