what is the value of x

Answer:
Assuming the other side is 30, x=12
Step-by-step explanation:
X+(X+6)=30
2x+6=30 (open the brackets by distributing the plus sign inside)
2x=24 (subtract 6 from both sides)
x=12 divide both sides by 12
This makes sense because of x is 6, and x+6 is 18, 6+18=30.
Answer:
x=4.5
Step-by-step explanation:
The triangles are similar (bases are parallel so bottom angles are equal (corresponding), hence they're similar by AA)
Since they're similar, their sides are in ratio:
(x+6)/(x+x+6)=(30-9)/(30)
(x+6)(30)=(2x+6)(21)
30x+180=42x+126
12x=54
x=4.5