plz help!!
will give the brainliest
need explanation.

Answer:
x =9
Step-by-step explanation:
A [tex]\cup[/tex] B =29
-->A = 29 -17 = 12
-->B = 29 -21 = 8
x=A [tex]\cap[/tex] B =A [tex]\cup[/tex] B - A - B= 29 - 12 - 8 = 9