Answer:
Jack sold 17 admission tickets and 12 vip tickets.
Explanation:
1. Let´s name the variables as:
x=number of admission tickets
y=number of vip tickets
2. As the problem says Jack sold a total of 29 tickets, it can be expressed as:
(Eq.1)
3. As the general admission tickets are $60, the vip tickets are $90 and he made $2100, it can be expressed as:
(Eq.2)
4. Solve for x on the Eq.1:
(Eq.3)
5. Replace Eq.3 in Eq.2:

6. Replace the value of y in Eq.3:

Therefore Jack sold 17 admission tickets and 12 vip tickets.