So how do we figure out that constant? Well, they have told us what f of two is. F of two is equal to 12. So let's write this down. So when, so f, so f of two is equal to 12, which is equal to, well, we just have to put two in everywhere we see an x. That's going to be negative two times two to the negative two power plus c. And so 12 is equal to, what is this? Two to the negative two.