Answer:

>! Jupiter = 578

Explanation:

>! The first digit is the position from the Sun (Mercury = 1, Venus = 2, etc.) so Jupiter = 5.  
>! The second digit is the length of the planet's name, so Jupiter = 7.  
>! To get the third digit, multiply the first and the second modulo 9; e.g. Venus $2 \times 5 = 10 \equiv 1 \pmod 9$. Therefore, Jupiter is $5 \times 7 = 35 \equiv 8 \pmod 9$.  

Also,

>! THAN is misspelled, it should be THEN.