To find the value of [tex]\( a \)[/tex] in the equation [tex]\( 3a + b = 54 \)[/tex] when [tex]\( b = 9 \)[/tex], follow these steps:
1. Substitute the value of [tex]\( b \)[/tex] into the equation:
Given the equation [tex]\( 3a + b = 54 \)[/tex] and knowing that [tex]\( b = 9 \)[/tex], substitute [tex]\( 9 \)[/tex] for [tex]\( b \)[/tex]:
[tex]\[
3a + 9 = 54
\][/tex]
2. Isolate the term involving [tex]\( a \)[/tex]:
To isolate [tex]\( 3a \)[/tex], subtract [tex]\( 9 \)[/tex] from both sides of the equation:
[tex]\[
3a + 9 - 9 = 54 - 9
\][/tex]
Simplifying this, we get:
[tex]\[
3a = 45
\][/tex]
3. Solve for [tex]\( a \)[/tex]:
To solve for [tex]\( a \)[/tex], divide both sides of the equation by [tex]\( 3 \)[/tex]:
[tex]\[
\frac{3a}{3} = \frac{45}{3}
\][/tex]
Simplifying this, we find:
[tex]\[
a = 15
\][/tex]
So, the value of [tex]\( a \)[/tex] is [tex]\( 15 \)[/tex]. The correct answer is:
```
15
```
