Output is produced according to Q = 4L + 6K, where L is the quantity of labor input and K is the quantity of capital input. If the price of K is $12 and the price of L is $6, then the cost minimizing combination of K and L capable of producing 60 units of output is:
Two solutions to help you:
1] An Excel solution using Excel Solver with an accompanying PNG image of the the Solver setup.
2] A PDF detailing a graphical solution.