Answer:
3 nC.
Explanation:
Let the charge be Q and it is situated at distance x from first point and
x + 3 from second point.
Applying formula for electric field we have , for first point
k Q / x² = 3
Applying formula for electric field we have , for second point
k Q / (x +3)² = .750
Dividing ,
(x +3)² / x² = 3/.750
= 4
(x +3) / x = 2
x = 3
Therefore the charge must be present at - ve 1 m . That is why its distance from x =2 m on + ve x axis is 3 m
Size of charge
k Q / x² = 3
Q = 3 x² / k
= (3 x 3²) / 9 x 10⁹
= 3 x 10⁻⁹
= 3 nC.