What is the electric potential midway between the two charges?

[sasuke07]

Homework Statement

Consider two equal positive charges (q=+2.0 µC) a distance of 3.0 cm apart. What is the electric potential midway between the two charges? What is the E field at this point?

I got the work and everything all solved out, i just don't know where some of the numbers came from. Where does the 2 before K come from, I understant the q= 2X10^-6, but why is r 1.5x10^-2? I am just wondering where some of the numbers came from.

Homework Equations

kq/r=E

The Attempt at a Solution

look at attachment

 

[tiny-tim]

hi sasuke07!

Where does the 2 before K come from, I understant the q= 2X10^-6, but why is r 1.5x10^-2? I am just wondering where some of the numbers came from.

that equation is kq_L/r_L + kq_L/r_L = 2kq/r …

they're defining q_R = q_L = q and r_R = r_L = r ​

(and r is half of 3.0 cm)