Iam completely lost on these things

Its pythagoras I think ^^; so 9^2 + 4.5^2 = 101.25 then square root it to get 10.0623059   just in future do a^2 + b^2 = c^2 (adjacent squared plus opposite squared gives you the longest side which is the hypotenuse squared) I hope that helps! ^^; 

The correct answer will be d. -4