A student wants to determine the gravitational attraction between two objects. Which two quantities does the student need to know?

a charge 3q is at the origin, and a charge −2q is on the positive x axis at x=a. part a where on the x-axis would you place a third charge so it would experience no net electric force? enter an expression for the exact answer, which will involve a square-root sign. (do not enter an approximate decimal answer.)

the answer is 12 as i may remember

: )