A college student completed some courses worth 3 credits and some courses worth 4 credits. The student earned a total of 59 credits after completing 18 courses. how many courses worth 3 credits did the student complete?
The answer is 13 because 13*3 = 39. 20 is impossible because that would total 60 credits. 5 isn't possible because then there would be no way to get 9 in the digits place.
