The answer is 1/2 the last one
F(-5) just means that your substituting the number -5 for every x value. So if you have x+1 this would be -5+1 which is -4
The easiest way to determine the score is to use a calculator or spreadsheet and the appropriate probability function.
If you want the top 10%, the score corresponds to the 90th percentile. That score is 316.
If you want the top 15%, the score corresponds to the 85th percentile. That score is 313.
2x+9=6x+7. 2x+2=6x. 2=4x. X=1/2 a year