Answer:
[tex]\huge\boxed{F.\ 44}[/tex]
Step-by-step explanation:
(look at the picture)
[tex]m\angle A+m\angle D=180^o\\\\m\angle A=42^o\\m\angle D=(3x+6)^o\\\\\text{substitute}\\\\42+3x+6=180\\\\3x+48=180\\\\3x+48-48=180-48\\\\3x=132\\\\\dfrac{3x}{3}=\dfrac{132}{3}\\\\x=44[/tex]
