二次方程數學

You can first list some cases out and observe the pattern
p = 160, q = 12000
p = 160 + 1 , q = 12 000 - 50(1)
p = 160 + 2 , q = 12 000 - 50(2)
........
p = 160 + n , q = 12 000 - 50(n)

Now, as you have to express q in terms of p, and you have q in terms of n
Then, find n in terms of p first
n = p - 160

Therefore, q = 12 000 - 50(n) = 12 000 - 50(p - 160) = 20000 - 50p

If you want to find also the total income, it would be
pq = p(20000 - 50p) = -50p^2 + 20000p = -50(p - 200)^2 + 2000000

a) q = 12000-50(p-160)
q=20000-50p
Explanation for reference:
since for every $1 increases in the ticket price, the number of tickets sold will decrease by 50, we first need to know how much is p higher than $160. Then, we times the increase of price by 50 and thus we find out the drop of the number of ticket sold. Finally, we subtract the drop of the no. of tickets sold form 12 000 (the maximum no.of tickets) and we can tell the actual number of tickets sold