.
Let k be the number of correct answers,  0 <= k <= 10.
Then the number of wrong answers is 10-k.
The formula for the score as the function of "k" is
    S(k) = 4k - (10-k) = 5k - 10.
So, when k =   0,  1, 2, 3,  4,  5,  6,  7,  8,  9, 10,  the values for S(k) are
             -10, -5, 0, 5, 10, 15, 20, 25, 30, 35, 40 .
Thus, 11 different values of scores are possible.
Solved.