We know that AB is perpendicular to CD. (that was given)
Perpendicular angles are 90 degrees because two straight lines (180) crossed make 4 90 degree angles.
180+180=360
90*4=360 See the similarities?
7x+6= 90 degrees
Subtract 6 on both sides.
7x=84
Divide both sides by 7.
x=12
"B" is the correct answer.
I hope this helps!
~kaikers
