4 spoons and 3 forks cost $15 4 spoons and 1 fork cost $13 how many do the forks cost?

Let's say that s=spoons and f=forks.

According to this, we can say that:

{4s+3f=15

{4s+f=13

This is a system.

We can then use elimination to solve and isolate the variable:

(4s-3f=15)

- (4s+f=13)

We can then subtract and conclude that:

-4f=2

-f=1/2

f=-1/2