thank you for your help!
my question is :how do you find the magnitude of the electric field that will balance the weight of an electron?
You need to know the strength of the gravitational field where the electron is located. If it is in lab on Earth, the electron's weight is
W = m g
Set m*g = e*E and you get
E = g*(m/e)
The units will be N/C (or volts/meter) if e is 1.6*10^-19 Coulombs, and m is the electron mass, in kg
g = 9.8 m/s^2