A charge of +80 µC is placed on the x-axis at x=0. A second charge of -50 µC is placed on the x-axis at x = 50 cm. What is the magnitude of the electrostatic force on a third charge of 4.0 µC placed on the x-axis at x = 30 cm?
a. 25 N
b. 77 N
c. 39 N
d. 45 N
e. 13 N