5a - b - a + 1/2b please jelp

Show me how you find y and determine what y is you i appreciate it : )

An appliance salesman sets a goal to sell an average of 6 appliances per day for the first two weeks of his new job. the dot plot shows the number he sold each day during the first 13 days. what is the minimum number of appliances he must sell on the 14th day in order to reach his goal? a) 5 b) 6 c) 7 d) 8

What’s the answer ? use the picture to see the problem