A) The constant is 7.5. FALSE. 7.5 is a coefficient, not a constant.
B) The coefficients are 7.5 and -9. FALSE. The coefficients are 7.5, -1/9 and 2. 50, being a constant, could be regarded as a coefficient in this case.
C) The variables are x and y. FALSE. There are three variables: x, y and z.
D) The like terms are 7.5y and 2y. TRUE. The variable (y) is the same in each term.
