Answer:
-4320
Explanation:
Using the formula for electric field between two points
E = kq/r²
The electric field at a midpoint, say x, is
E(x) = [(k * 16.7*10^-9)/0.5²] - [(k * 47.3*10^-9)/0.25²]
E(x) = [k * (16.7*10^-9 - 47.3*10^-9)/0.25²]
E(x) = [(k * -30.6*10^-9)/0.0625]
E(x) = [(9*10^-9 * -30.6*10^-9)/0.0625]
E(x) = -270/0.0625
E(x) = -4320
Therefore, we can conclude that the electric field, halfway in between them is -4320