Let's call the number of subscribers that Jonah signs up "x". Each new subscriber reduces Jonah's monthly cost by $0.75, so his monthly cost can be expressed as:
14.99 - 0.75x
We want to find how many subscribers Jonah needs to sign up in order to bring his monthly cost down to $5.00 or less. So we can set up the following inequality:
14.99 - 0.75x ≤ 5
Solving for x, we get:
0.75x ≥ 9.99
x ≥ 13.32
Since Jonah can't sign up a fraction of a subscriber, we need to round up to the nearest whole number. Therefore, Jonah needs to sign up at least 14 new subscribers in order to bring his monthly cost down to $5.00 or less.