Here are the step for solving this:
1. 3y + 5 > 23
-5 -5
3y/3 > 18/3
y > 6
In words what you are doing is getting y by itself on one side. Subtract the 5 to undo the adding of 5 first. Then, divide both sides by 3.
He payed 0.72
First you take 2.88, then you multiply it by 1/4 or a simpler way would be to divide 2.88 by 4. The answer is $0.72
I don't think anyone can solve this without seeing the table mentioned in the question :)
D1 = 60 for a price of $80. Charging $80 will ensure supply exceeds demand.
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The store apparently could charge a price slightly lower than $80, but we cannot tell from the chart how much lower.