The expression for the magnitude of the electric field of a point charge is E = kq/r2 (We have assumed that the dielectric constant is 1)

 The fields and their components are shown in the figure.
 
 

Ex = E2x - E3x = (2.25 - 1.59)X104 = 0.66 X104 N/C
Ey = E3y = 1.59X104 N/C
E = (Ex2 + Ey2)½ = [(0.66)2 + (1.59)2]½X104 = 1.72X104 N/C

q = tan-1 Ey/Ex = tan-1 1.59/0.66 = 67.5º

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