We can form two equations, let the price of a senior ticket be s and the price of a child ticket be c. 
We have from day 1: 
A: 3s + 9c = 75 
And from day 2: 
B: 8s + 5c = 67 
 
Now we can rewrite A as: 
A: 24s + 72c = 600 
And can rewrite B as: 
B: 24s + 15c = 201 
 
Now A-B can be written as: 
A-B: 57c = 399 
 
So c = 7 
 
Now substituting this back into A we get: 
A: 3s + 63 = 75 
A: 3s = 12 
 
So s = 4 
 
We have the price of a senior ticket is $4 and the price of a child ticket is $7 (idk if this is right hope it is!!!)