A -2.8 nC charge is on the x-axis at x₁ = -8 cm and a 3.6 nC charge is on the x-axis at x₂ = 15 cm. What is the electric field at the point x = 0 on the x-axis due to these charges?
(a) E = 3.6k² / 15² N/C
(b) E = 2.8k² / 8² N/C
(c) E = (3.6 - 2.8)k² / (15 + 8)² N/C
(d) E = (3.6 + 2.8)k² / (15 - 8)² N/C