Let 32.9 × 10^-6 s be the total time of radiowaves going back and forth, Let X be the time going down and (32.9 × 10^-6) - X the time going back. We assume the distance going forward and back is equal, we use the formulas: X = VoT + (1/2)AT^2 and V = D/T. Substituting the values: (1/2)(9.8 m/s^2)(4 - X)^2 = (1.7 × 10^8 m/s)(X) --> Using the calculator, we find: X = 4.40 × 10^-7. Then we multiply with the speed to find the depth of the ice: 74.8 m.