It's asking how far horizontally from the starting point which means that y, the height in meters is 0.
set 0 = -0.06x^2 + 10.1x + 5 and solve for x using the quadratic formula
-b +-

/ 2a
-10.1 +-

/ 2(-0.06)
you get that x = 168.83 m and -0.49 meters. Since the horizontal distance cant be negative, 168.83m is your answer