I need help with part b. I have completed some of b but when I click on "bin" under add constraint in solver of Excel it pop up with the message: "binary constraint cell reference must include only variable cells"

Excel document: https://1drv.ms/x/s!AoQGMTkNnGG_hxmKZXpfw9ncFRCQ

In solver under Subject to constraints, the third one down should be $G$6:$G$11=Binary and evertime I click Bin under the add button I get the message: "binary constraint cell reference must include only variable cells"

14.Radford Castings can produce brake shoes on six different machines. The following table summarizes the manufacturing costs associated with producing the brake shoes on each machine along with the available capacity on each machine. If the company has received an order for 1,800 brake shoes, how should it schedule these machines?

a. Formulate an ILP model for this problem.

b. Create a spreadsheet model for this problem and solve it.

c.What is the optimal solution?

Machine Fixed Cost $1000 $ 950 $ 875 $ 850 $ 800 $ 700 Variable Cost $21 $23 $25 $24 $20 $%26 Capacity 500 600 750 400 600 800 2 3 4 Machine Fixed Cost $1000 $ 950 $ 875 $ 850 $ 800 $ 700 Variable Cost $21 $23 $25 $24 $20 $%26 Capacity 500 600 750 400 600 800 2 3 4