Answer:
13.71 m
Step-by-step explanation:
Draw the tunnel so the width marks the zeroes at (-12,0) and (12,0)
then y = a ( x+12)(x-12) is the equation..
..to calculate 'a' sub in the point 9, 6 (where the width is 18)
6 = a ( (9+12)(9-12) shows a = -2/21
y = -2/21 (x+12)(x-12) Max is when x = 0
-2/21 ( 12)(-12) = 288/21 = 13.71 m
