Answer
Complement of $ 120^{\circ}$ = - $30^{\circ}$
Supplement of $ 120^{\circ}$ = $60^{\circ}$
Work Step by Step
Complement of $ 120^{\circ}$ = $ 90^{\circ} - 120^{\circ}$ = - $30^{\circ}$
(As sum of the measures of complementary angles is 90 degrees, we can find 'one' by subtracting 'other' from $90^{\circ}$ )
Supplement of $ 120^{\circ}$ = $ 180^{\circ} - 120^{\circ}$ = $60^{\circ}$
(As sum of the measures of supplementary angles is 180 degrees, we can find 'one' by subtracting 'other' from $180^{\circ}$)