Solve this exercise

The angle given as $120^\circ$ is in the position of angle $d$. Angles $a$ and $d$ are adjacent angles on a straight line, so their sum is $180^\circ$.

$$a + d = 180^\circ$$ $$a + 120^\circ = 180^\circ$$

$$a = 180^\circ - 120^\circ$$ $$a = 60^\circ$$

Angles $b$ and $d$ are vertically opposite angles. Vertically opposite angles are equal.

$$b = d$$ $$b = 120^\circ$$

Angles $c$ and $a$ are vertically opposite angles. Vertically opposite angles are equal.

$$c = a$$ $$c = 60^\circ$$

The values are:
$a = \boxed{\text{60}^\circ}$
$b = \boxed{\text{120}^\circ}$
$c = \boxed{\text{60}^\circ}$
$d = \boxed{\text{120}^\circ}$