Answer:
no. of senior citizens=x
no.of other people=7-x
cost=30=k(7-x)+(k/2)x. k is the cost of a ticket
k(7-x+x/2)
k(7-x/2)-30=0
k=60/(14-x)
now do trial and error substitution for (x<7) until u get a whole number for k also (k<30). if you have the skills you can suggest the number yourself
ie x= 2, k=5$