Explanation:
To find the common difference \( d \) in an arithmetic sequence with \( 25 \) terms, where the first term \( a_1 = 60 \) and the last term \( a_{25} = -12 \), use the formula for the \( n \)-th term of an arithmetic sequence:

\[
a_n = a_1 + (n - 1) \times d
\]

Here, \( n = 25 \), \( a_1 = 60 \), and \( a_{25} = -12 \). We need to find \( d \).

Step-by-Step Solution:

1. Substitute the known values into the formula for the 25th term:

\[
a_{25} = a_1 + (25 - 1) \times d
\]

\[
-12 = 60 + 24 \times d
\]

2. Solve for \( d \):

\[
-12 - 60 = 24 \times d
\]

\[
-72 = 24 \times d
\]

\[
d = \frac{-72}{24} = -3
\]


The common difference is -3.

The correct answer is C. -3.