You're nearly there. Just some more steps. 557 * x = 594 tells us x = 594 / 557 (divide both sides by 557) x ≈ 1.066427
When we've found this number we must realise the following: the '1' in this answer is the 100% the car fixing costs (without taxes) the '0.66427' stands for the tax rate.
To find the tax rate we multiply 0.66427 by 100, which gives us: 0.66427 * 100 = 6.6427 ≈ 7