I found the magnitude of the magnetic field but I cannot understand how can we sure about the direction of it.

17. A negatively charged particle enters a uniform magnetic field at right angles and follows the path shown. -q If q=-4x10 6C, mass= 8x10-2kg, radius of path r=2cm, and velocity of particle is V=100m/sec, find the magnitude and direction of the magnetic field. B 2, 102_ 8 x 1072 x 102 2 = 21 10-2 146