Suppose Julia and Zach are the only consumers of milk. Julia's demand for milk is defined as QdJulia = 60 - 3P at prices below $10 and zero for prices above $10. Zach's demand for milk is defined as QdZach = 40 - 2P at prices below $20 and zero for prices above $20. If the market price for milk is $15.13, market demand is: (Round to the nearest whole unit of milk)