Given that e parallel f and g is a transversal, we know that angle 4 is-congruent-to angle 5 by the alternate interior angles theorem. We also know that angle 1 is-congruent-to angle 4 and angle 5 is-congruent-to angle 8 by the ________. Therefore, angle 1 is-congruent-to angle 8 by the substitution property.