Given that AB and EF have a common transversal, GJ, we have;
Given that AB is parallel to EF, we have;
Line AB || line EF
mELJ = 120° given
mELJ + mELK = mBKL + mGKB; Transitive property of equality
mELJ + mELK = mELK + mGKB
mELJ = mGKB
mGKB = 120° by substitution property
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