To solve this problem you must apply the proccedure shown below:
 1. You have that:
 - He sales 13 gold rings and 18 silver rings in 9405 euros.
 - The cost of the silver ring is three times the cost of the gold ring.
 2. Keeping the information above on mind, you have the following system of equations:
 x: the gold ring.
 y: the silver ring.
 x+y=9405
 x=3y
 3. Then, you have:
 (3y)+y=9405
 y=9405/4
 y=2351.23 euros
 x=3y
 x=3(2351.23)
 x=7053.75 euros
 The answer is:Â
 - Gold ring=7053.75 euros
 - Silver ring=2351.23 euros
