There are 18 students in mr. alvarez’s art class. throughout the year, every student must pair up with every other student to complete a project. how many projects will be finished?
a. 149 projects
b. 153 projects
c. 171 projects
d. 135 projects

To my knowledge it would be:
B. 153 projects

The first one, i believe, would be correct. all the others have one thing in common, and that's that they have repeating numbers. in the second one, x and y have repeating 6's and 3's, and in the third, x and y have repeating 6's as well. in the last one, there are repeating 3's. the first one has no repeating numbers.