If you know that xlogxa = a, then after dividing both sides by 3, xlogx7 = xln10/3
So, 7 = xln10/3
Raising both sides by 3/ln10 gives x = 73/ln10
This is your first misunderstanding. You can't 'solve' ln10 - this is just a number, like the number 200, you can't solve just that number.
You...