ANSWER
106 3rd graders
EXPLANATION
Let the number of 2nd graders be x.
Let the number of 3rd graders be y.
We have that there are 39 fewer 2nd graders than 3rd graders. This means that:
x = y - 39
There are 67 2nd graders. This means that:
x = 67
This means that:
67 = y - 39
y = 67 + 39
y = 106
Therefore, there are 106 3rd graders.
