Answer:
39 lessons
Explanation:
You want to write and solve an equation for the number of lessons Emmett took if he paid a total of $712 for lessons costing $18 each, and a $10 registration fee.
Equation
The total cost is the sum of the individual costs.
The cost of n lessons at $18 each is 18n.
The registration fee is 10.
The total cost is 712, which is the sum of these:
712 = 10 + 18n . . . . . . . an equation for the number of lessons
Solution
Subtracting 10 gives ...
18n = 702
Dividing by 18, we have ...
n = 39
Emmett took 39 lessons in the year.
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Additional comment
Often, when you are asked to write an equation expressing some relationship, a relevant equation will be one that shows the total is the sum of the parts.
The exceptions are rare, and almost never encountered in high school math.