I want to make NPC that exchange : 10 mithril = 1 bronze coin
20 mithril = 1 silver coin
30 mithril = 1 gold coin
50 mithril = 1 mithril coin
20 mithril ore = 1 bronze coin
30 mithril ore = 1 silver coin
40 mithril ore = 1 gold coin
60 mithril ore = 1 mithril coin
Please help me !!