it's worth thinking if they put that money in a basic account with 5% interest (I get 4.5% in one of my accounts and 5.2% in another, so I'll simplify), with $24k in there, that would be $100 per month, or 20% of their monthly budget.
7% is quite common with basic etfs, but it's more annoying to move money back to pay bills then. My point is: this could/should last even longer. Money which doesn't increase in value, loses value (inflation).