The problem can be expressed in the following system of linear equations:
A total of 120 adults (a) and students (s) attended a school:
a + s = 120
Each adult paid $2.50, mathematically, that is 2.5a
Each student paid $1, mathematically, that is 1s
and the total paid by adults and students attending the game was $189
then, we have:
2.5a + 1s = 189
then, we can conclude that the problem can be expressed as follows:
a + s = 120
2.5a + 1s = 189
or equivalently:
a + s = 120
2.5a + s = 189
so, the correct answer is D.