To find the value of the expression [tex]\(21 - 2a\)[/tex] when [tex]\(a = 3\)[/tex], follow these steps:
1. Substitute [tex]\(a = 3\)[/tex] into the expression:
[tex]\[
21 - 2a \rightarrow 21 - 2(3)
\][/tex]
2. Multiply [tex]\(2\)[/tex] by [tex]\(3\)[/tex]:
[tex]\[
2 \times 3 = 6
\][/tex]
3. Subtract [tex]\(6\)[/tex] from [tex]\(21\)[/tex]:
[tex]\[
21 - 6 = 15
\][/tex]
Therefore, the value of the expression [tex]\(21 - 2a\)[/tex] when [tex]\(a = 3\)[/tex] is [tex]\(15\)[/tex].
So, the correct answer is:
B. 15
