Let's define the variables:
- Let \( A \) be the number of students taking a math course.
- Let \( B \) be the number of students taking a language course.
- Let \( X \) be the number of students taking both math and language courses.
We know that:
- \( A = 140 \)
- \( B = 145 \)
- The number of seniors taking either math or language (or both) is given as 75% of the total seniors. Therefore:
\[ \text{Number of seniors taking a math or language course} = 0.75 \times 300 = 225 \]
We can use the principle of inclusion-exclusion to express the total number of students taking at least one of the courses:
\[ A + B - X = \text{Number of seniors taking math or language course} \]
Substituting the values we have:
\[ 140 + 145 - X = 225 \]
Combining the numbers:
\[ 285 - X = 225 \]
Now we solve for \( X \):
\[ -X = 225 - 285 \] \[ -X = -60 \] \[ X = 60 \]
Therefore, the number of seniors taking both a math and a language course is 60.