Un joyero vende 13 anillos de oro y 18 de plata por 9405 euros. sabiendo que el anillo de oro cuesta el triple que el de plata ¿cual es el precio de cada anillo?

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: 
 - Gold ring=7053.75 euros
 - Silver ring=2351.23 euros

Num of plants = (original#ofplants)*(1.6)^t