Step-by-step explanation:
To find the electric force that is acting between two charges we can use the Coulomb's Law.
Fe = k * q₁ * q₂/r²
Where q₁ is quantity of charge of the charge number 1, q₂ is the quantity of charge of the charge number 2, k is the Coulomb's law constant (9.00 x 10^9 N-m²/C²) and r is the distance between the two charges. We already know these values.
q₁ = 0.0042 C
q₂ = 0.0050 C
k = 9.00 x 10^9 N-m²/C²
r = 0.0030 m
We can replace these values in the formula and get the answer to our question.
Fe = k * q₁ * q₂/r²
Fe = 9.00 x 10^9 N-m²/C² * 0.0042 C * 0.0050 C/(0.0030 m)²
Fe = 2.1 *10^10 N
Answer: a. 2.1 *10^10 N