The <em>correct answer</em> is:
4 points per multiple choice question
Explanation:
Let x be the amount each multiple choice question is worth. Since Gretchen answered 18 of them correctly, we would write this as 18x. Adding the 19 points for the essay question, we have 18x+19.
Since Ezia answered 15 multiple choice questions correctly, we would write this as 15x. Adding the 31 points for the essay question, we have 15x+31.
Since they had the same score, we set these equal to one another:
18x+19 = 15x+31
To solve this, first subtract 15x from each side:
18x+19-15x = 15x+31-15x
3x+19 = 31
Subtract 19 from each side:
3x+19-19 = 31-19
3x=12
Divide each side by 3:
3x/3 = 12/3
x = 4
Each question is worth 4 points.