A manufacturing plant produces metals for various industrial applications. It costs $6000 to make 10 pounds of titanium, and $13,500 to make 25 pounds. It costs $1,500 to make 10 pounds of cobalt, and $3000 to make 25 pounds. Each pound of titanium sells for $600, and each pound of cobalt sells for $150. Suppose the company sold 5 pounds of titanium and some (unknown) number of pounds of cobalt, and reached their breakeven point. How many pounds of cobalt did they sell?