answer is D.
1) plug in 6 and 7. u know 6 is the only one. Suff.
2) u get x > 5. from the stem, u get 4 < n < 7. so n can only be 6 here. Suff.
for the 2nd statement, can you please show the actual step of how you flipped it and got the range for n?
I know you manipulated it with 1. but just want to make sure that I get this.