Question 1131850
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Using formal algebra on this problem is good exercise in learning how to solve problems using algebra.<br>
However, note that the formal algebraic solution does exactly what you can do informally with logical reasoning.<br>
The difference between the two purchases was 2 additional kg of gummy bears for an additional $18; that means the cost of the gummy bears is $9 per kg.<br>
Then, knowing that, you can use either of the purchases to find the cost per pound of the cinnamon red hots.  For example, Erika bought 3 kg of cinnamon red hots and 1 kg of gummy bears for $21; the gummy bears cost $9, so the 3 kg of cinnamon red hots cost $12; so the cinnamon red hots cost $4 per kg.