It would be 9/25. First you find the common denominator which is 25 so then you convert 1/5 to 5/25 so now you have 4/25+5/25 which you would get 9/25 and since 9 can only be divided be 3 and 25 can't your answer would be 9/25.
We can calculate using cosinus method in triangle c² = a² + b² - 2ab cos c
Plug in the number to the formula c² = a² + b² - 2ab cos c c² = 10² + 8² - 2(10)(8) cos 105° c² = 100 + 64 - 160 cos 105° c² = 164 - 160 (-0.26) c² = 164 + 41.6 c² = 205.6 c = √205.6 c =14.34
