End game ranking

so,you did good. very good. you had fun,you tilted your opponent jungler ( of all things.) and got an A. an A!? I was 10/3/17 . How do kills and assist count into ranks? I don't know... My stats: 10/3/17 117 CS and 14,330 gold The person that got an S-: 4/4/22 18CS 14,306 gold I was 5 less assists but had 6 more kills and one death off other stats largest killing spree (I will be the first number the other morgs) 4/2 largest multi was 1/1 I got first blood(and no it was not KS it was a legitimate kill in the jungle.... ) total damage altogether (rounded to lowest thousand) 159K/44K our was 135K... I don't care for chests as the keys will be a pain to get,but idk how morg did more :/ if she shielded an ally that gets her an assist,but I also have a lot of assists. the only thing morg outdid me on was assists by 5 and magic damage to champs by 3K...plus like 75. ward/control wards placed by 15(I get rank from that but I still don't get how i was an A)and towers destroyed (she got one and I got an inhibitor) But overall a great game. we lost two towers,got 10 of theirs a baron,and all dragons available at the time (3 to be specific) and not a single toxic person besides the salty ramus...stole like 5 of his buffs and cleared 36 of his jungle camps xD