Given:
In parallelogram PQRS, [tex]m\angle Q=(20+2x)^\circ,\ m\angle R=6x^\circ[/tex].
To find:
The value of x.
Solution:
In a parallelogram, the consecutive interior angles are supplementary angles.
In parallelogram PQRS,
[tex]m\angle Q+m\angle R=180^\circ[/tex] (Supplementary angles)
[tex](20+2x)^\circ+(6x)^\circ=180^\circ[/tex]
[tex](20+8x)^\circ=180^\circ[/tex]
[tex]20+8x=180[/tex]
Subtracting 20 from both sides, we get
[tex]8x=180-20[/tex]
[tex]8x=160[/tex]
Divide both sides by 8.
[tex]\dfrac{8x}{8}=\dfrac{160}{8}[/tex]
[tex]x=20[/tex]
Therefore, the correct option is C.