Substituting the given value of
y=18 into the equation
x=y yields
x=()(18),or
x=12.. The value of the expression
2x−3 when
x=12 is
2(12)−3=21. Choice B is incorrect. If
2x−3=15, then adding 3 to both sides of the equation and then dividing both sides of the equation by 2 yields
x=9. Substituting 9 for x and 18 for y into the equation
x=y yields
9=18=12,which is false. Therefore, the value of
2x−3 cannot be15. Choices C and D are also incorrect. As with choice B, assuming the value of
2x–3 is 12 or 10 will lead to a false statement.