HELPPP I DONT UNDERSTAND

Answer:
[tex]\boxed{\bf \angle B = 58^{o}}[/tex]
Step-by-step explanation:
The cyclic quadrilateral sum of the opposite angle is 180°. From the given figure....
[tex]\bf \angle B + \angle D= {180}^{o} [/tex]
Where....
~[tex]\bf \angle B = 3x+7[/tex]
~[tex]\bf \angle D = 6x+20[/tex]
Now, that we found x, let's find angle B....
[tex]\sf Therefore, \: \boxed{\sf \angle B = 58^{o}}[/tex]