Let \( x \) be the number of points each multiple choice question is worth.
Gretchen's total score can be expressed as: \[ \text{Gretchen's score} = 18x + 19 \]
Ezia's total score can be expressed as: \[ \text{Ezia's score} = 15x + 31 \]
Since their scores are equal, we can set up the equation: \[ 18x + 19 = 15x + 31 \]
To solve for \( x \), first, subtract \( 15x \) from both sides: \[ 18x - 15x + 19 = 31 \] This simplifies to: \[ 3x + 19 = 31 \]
Next, subtract 19 from both sides: \[ 3x = 31 - 19 \] Which simplifies to: \[ 3x = 12 \]
Now, divide both sides by 3 to solve for \( x \): \[ x = \frac{12}{3} = 4 \]
Thus, the value of each multiple choice question is: \[ \boxed{4} \text{ points} \]