To start the control would be import to see how drivers would act with full focus on the road. The subjects should (in order for the only difference to be the phone) is to use the same vehicle same road same weather condition, just obviously one has the phone the other does not. I hope this helps
magnetic field due to a finite straight conductor is given by

here since it forms an equilateral triangle so we will have

also the perpendicular distance of the point from the wire is

now from the above equation magnetic field due to one wire is given by



now since in equilateral triangle there are three such wires so net magnetic field will be

If you multiply m (the unit for wavelength) with 1s (the unit for frequency), you will get m/s, the unit for speed. Now multiply! 25 m/s is your final answer!
I believe it’s A. I know for sure it isn’t D.