Answer:
X=1
Step-by-step explanation:
6x+12-3=15
6x+9=15
6x+9-9=15-9
6x=6
X=1
Associative property of addition
Answer: 33.75
Step-by-step explanation:
It’s right
Based on the calculations, the unknown number is equal to 
- Let the unknown number be x.
<h3>How to find an
unknown number:</h3>
Translate the word problem into an algebraic expression, we have;
Adding 21 to the unknown number:

Multiplying the result by 3:

84 more than two-thirds of the unknown number:

Equating the equations, we have:

Cross-multiplying, we have:

Read more on word problems here: brainly.com/question/13170908