This is for 20 !
the cost of having photos taken includes a sitting fee and $12 for each portrait. the cost of 3, 6, and 9 photos respectively is $51, $87, and $123. what is the sitting fee?
a. $13
b.$15
c.$27

All really need to do is pick one number. so, we will go with 6 and 87.

6 times 12 is 72 then you subtract that from $87.

That would be 15

To double check, you can use another one. 9 and 123.

9 times 12 is 108. subtract that from 123 and you get 15.

Your answer is B) $15

Hope I helped :)

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step-by-step explanation: