Mei and Kara build computers from parts and sell them to make a profit. Mei can build a computer in 0.9 hour, and kara can build one in 1.2 hours. One week, Mei builds twice as many computers, and the two spend a total of 24 hours on their project. During a typical week, Mei and Kara spend 15 hours building computers. How many computers do they each make during a typical week?