Ling wants to save $87 for tickets to a rock concert if she has $23 now and will save $4 per week how long it take her to get enough money to buy the tickets

In this case we have that the total cost of the tickets is $87.If she is $23, then she is missing:

He is missing $64.

If you can save $4 per week we have:

Where "x" represents the number of weeks to work:

So, Ling must work at least 16 weeks to get the money he needs for concert tickets.

16 weeks