Answer:
C. Add 9 to both sides of the equation.
Step-by-step explanation:
Given

Required
Complete the squares
We have:

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Take the coefficient of -6 i.e. -3
Square it (-3)^2 = 9
Add 9 to both sides
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<em>Hence, C is correct</em>
4) because 10 x 10 is 100
13.25 cases but round that up to 14 cases to transport 159 items. 159÷12=13.25