3.) I'm trying to see if I got this answer right. If not, correct me.

Total cost of energy drinks ($4.50) = y
Total number of energy drinks (3) = x
Equation = ?
To find this we need to find the cost of 1 drink = 4.50 ÷ 3 = $1.50.
So, the equations are :-
y = 1.50x
x = 4.50/y
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Yes, your answer is correct :)
You can use the 2nd equation too.
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