as coefficients are real one of the roots is -1/2 + root3 / 2 i
from here times z1 by z2 and by using the factor theorem z1xz2xz3xz4=e/a
and z1+z2+z3+z4=-b/a both z3 and z4 can be found
by the way left the working for you as doing the question yourself is much better for your learning...