I am having trouble solving this question based on my notes - can you explain further?

Three charges are arranged in the (r, y) plane as shown. y (m) 10 -7 nC T3 nC O- 8 nc 0 1 2 3 4 5 6 7 8 9 10 (m) What is the magnitude of the resulting force (in nano-Newtons) on the 3 nC charge at the origin? The Coulomb constant is 8.98755 x 10" N . m?/C2. Answer in units of nN. What angle does the resultant force on the 3 nC charge at the origin make with the pos- itive r axis? Quadrant I lies between 0" and 90", quadrant II between between 90" and 180, etc. Answer in units of degs