the probability to get a number less than 11 is 33/36, to get an 11 is 2/36 and to get an 12 is 1/36. if we want the game to be fair, the expected value should be 0, so we get
[tex]-2\cdot\frac{33}{36}+4\cdot\frac{2}{36}+\frac{c}{36}=0\rightarrow-66+8+c=0\rightarrow c=66-8=58[/tex]