Answer
$ E = 2.4 \times 10^{4} N/C $
Work Step by Step
We know that:
$F = qE \\\\
E = F/q$
We also know:
$F = 3.9 \times 10^{-15} N $
$q = e = 1.6 \times10^{-19} C $
We plug in the known values to obtain:
$ E = 2.4 \times 10^{4} N/C $