So a property of parallelograms is that consecutive angles are supplementary, or add up to 180. Using this information, this is our equation: [tex] 30+5x+15+10x=180 [/tex]
Firstly, combine like terms: [tex] 15x+45=180 [/tex]
Next, subtract 45 on both sides of the equation: [tex] 15x=135 [/tex]
Lastly, divide both sides by 15 and your answer is x = 9, or D.
