Let p = Thompson teaches this course.
Let q = I will get a passing grade.
Then the symbolic form should be ~q --> ~p. Completely valid!
Here's why...
p......q......~q......~p......~q --> ~p
T......T.......F........F..............T
T......F.......T........F..............F
F......T.......F........T..............T
F......F.......T........T..............T <---
Notice it is logically equivalent to p --> q (i.e., the truth table of ~q --> ~p is the same as the truth table of p --> q).