Partial answer:

Jupiter = 57x

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.

Also,

THAN is misspelled, it should be THEN.

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.