A child walks on a level surface from point P to point Q at a bearing of 30^o, from point Q to point R at a bearing of 90^o and then directly returns to the starting point P at a bearing of 240^o. The straight-line paths PQ and QR are 4 m each. Assuming that all bearings are measured from the magnetic north in degrees, the straight-line path length RP (in meters) is _______. (rounded off to the nearest integer).