QuestionUse the given information and theorems and postulates you have learned to show that $c \| d$.
18. $\mathrm{m} \angle 4=58^{\circ}, \mathrm{m} \angle 6=58^{\circ}$
19. $\mathrm{m} \angle 1=(23 x+38)^{\circ}, \mathrm{m} \angle 5=(17 x+56)^{\circ}, x=3$
20. $\mathrm{m} \angle 6=(12 x+6)^{\circ}, \mathrm{m} \angle 3=(21 x+9)^{\circ}, x=5$
21. $\mathrm{m} \angle 1=99^{\circ}, \mathrm{m} \angle 7=(13 x+8)^{\circ}, x=7$