The range of r is -2 to 5, which is 8 integers including zero.
The range of k is 2 to 7 which is 6 integers.
The total number of combinations of r and k is therefore 8*6=48.
If 0 counts as an integer then there are 6 quotients with 0 as numerator.
Only the following (r,k) pairs produce integer quotients: (-2,2), (2,2), (3,3), (4,2), (4,4), (5,5).
Therefore we have a total of 12 (r,k) pairs out of 48 possibles. the probablity is therefore 12/48=1/4.
If zero doesn't count as an integer the probability is 6/48=1/8.