To solve the equation and determine the first number [tex]\( n \)[/tex]:
1. Start with the given equation:
[tex]\[
2n + 1 = 157
\][/tex]
2. Isolate the term with [tex]\( n \)[/tex] by subtracting 1 from both sides of the equation:
[tex]\[
2n + 1 - 1 = 157 - 1
\][/tex]
Simplifying this, we have:
[tex]\[
2n = 156
\][/tex]
3. Solve for [tex]\( n \)[/tex] by dividing both sides of the equation by 2:
[tex]\[
n = \frac{156}{2}
\][/tex]
Simplifying this division:
[tex]\[
n = 78
\][/tex]
Therefore, the first number [tex]\( n \)[/tex] is [tex]\( 78 \)[/tex].
So, the correct answer is:
B. 78
