i used the answer key to get my answer and checked it with my dumb useless teacher and it’s right but, he won’t tell me how to get the numerators like how does it go from 3 & 7 to 15 & 14 please help omg!!!!

i used the answer key to get my answer and checked it with my dumb useless teacher and its right but he wont tell me how to get the numerators like how does it class=