I think x=8
8/4 = 2
16/2 = 8
You're very close. However, the less steep line should go through (4,7) and not some point slightly above that location. Also, the shaded region should be above both dashed lines at the same time. So you won't include the portion that I've marked in blue (see attached). Other than that, it looks great.
Answer: the answer is 0.35 because
Square root of 546 is 23.3666428911
23.3666428911 divided by 67 is 0.34875586404
0.34875586404 rounded to 2 decimal points is 0.34875586404