He should use 3/5 80% solution to achieve the desired quantity, or 18 mL of 80% solution and 12 mL of 60% solution. This has a total of 60%*12+80%*18=21.6 mL solution, which is equal to the desired 72%*30=21.6 mL solution.
5/6 1/4 2/3 1/2 Sorry i am bad at math too
The answer is $74.88 cause $5.76 times 13 is $74.88