Question 967169
The question about the Sixth and Eigth graders is now already answered and explained.  


The next question about Jesse's and Tanya's ages:
A direct transcription according to the description is, 
{{{-15+J=6+T}}}, using J for Jesse's age and T for Tanya's age.  You can convert, using simple algebra, to whichever form you need and check which card matches.