To find the value of the expression [tex]\(21 - 2a\)[/tex] when [tex]\(a = 3\)[/tex], follow these steps:
1. Substitute the given value of [tex]\(a\)[/tex] into the expression. Here, [tex]\(a = 3\)[/tex].
So, the expression becomes:
[tex]\[
21 - 2 \times 3
\][/tex]
2. Perform the multiplication first, as per the order of operations (also known as PEMDAS/BODMAS rules).
Multiply [tex]\(2\)[/tex] by [tex]\(3\)[/tex]:
[tex]\[
2 \times 3 = 6
\][/tex]
3. Subtract the result from [tex]\(21\)[/tex]:
[tex]\[
21 - 6 = 15
\][/tex]
Thus, after performing these steps, the value of the expression [tex]\(21 - 2a\)[/tex] when [tex]\(a = 3\)[/tex] is [tex]\(15\)[/tex].
So, the correct choice is:
B) 15
