Answer:
the correct answer for that would be identity property
3a+9=54
3a+9-9=54-9
3a= 45
a=15
Check answer:
3(15)+9=54
54=54
Answer is a=15
3rd side length can being choice B. 4 ,C. 7,F. 10, E. 12,
Step-by-step explanation:
brainly.com/question/1451975