Answer
$1.02\times10^{-7}N/C$
Work Step by Step
Set the magnitudes of the gravitational and electric forces equal to each other; solve for the field strength.
$$F_{electric}=F_{gravitational}$$
$$qE=mg$$
$$E=\frac{mg}{q}$$
$$E=\frac{(1.67\times10^{-27}kg)(9.80m/s^2)}{1.602\times10^{-19}C}=1.02\times10^{-7}N/C$$
Gravity pulls down, so the electric field must point up so that the positively charged proton feels an upward force.