Hi there!
Recall the following equation relating electric force to electric field:
[tex]F_E = qE[/tex]
[tex]F_E[/tex] = Force due to electric field (N)
[tex]q[/tex] = Charge of particle (C)
[tex]E[/tex] = Electric Field Strength (N/C)
Rearrange to solve for the Electric Field, and solve.
[tex]E = \frac{F_E}{q} = \frac{123}{0.7} = \boxed{175.714 \frac{N}{C}}[/tex]
