Constraints describe the limitations on the amount of resources available to optimize the objective function. In the Constraints panel, add whatever Constraints are applicable to the problem.
Click the + symbol to add a constraint, and the “clear constraints” button 
to remove all constraints:
Click on Name to give a name to the constraint.
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Enter a cell reference in the first box, to represent the resource that is limited in this constraint. The cell is highlighted in the grid once specified.
If a range of cells is subject to the same constraint, you can enter that cell range here, rather than create a different constraint for each cell.
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The relational operator can be >= (greater than or equal to), <= (less than or equal to), or = (exactly equal to). Choose one from the dropdown list.
A constraint such as 0 ≤ a16 ≤ 1000 must be expressed as two separate constraints: a16 >= 0 and a16 <= 1000.
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Enter a quantity in the final box:
You can alternatively enter a cell reference here, or a range of cells, as in a. above, if that range of cells represents a set of similar constraints.
Note: The more constraints are added to the problem, the longer it might take to solve.
Examples
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Flour <= 1000000 represents a constraint on a cooking ingredient with limited resources.
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Pies >= 100 represents a minimum quantity that must be produced.
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T = 40 represents the average time per week that a worker is available to work, where T is the number of hours.
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