Answer:
25 adults and 30 students
Explanation:
Let x be the number of adults and y be the number of students that visited the museum in one day. Then

x adults pay $20x and y students pay $20·0.6·y (because the the admission fee was reduced by 40%, then the admissin fee bacame $20·(1-0.4)=$20·0.6 ).
Thus,

Therefore, you have to solve the system of two equations:

From the first equation
substitute it into the second one:

and
