(6/2) - 4 would be your answer
Your sequence appears to be geometric with a common ratio of 2. It can be described by
a(n) = (-2 2/3)·2^(n-1)
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This can be written in a number of other forms, including
a(n) = (-8/3)·2^(n-1)
a(n) = (-1/3)·2^(n+2)
a(n) = (-4/3)·2^n
You earn $15 per lawn. 1 lawn would be $15. 15(1) is 15.
7 lawns would be 15(7), which is 105.
One solution ! Which is x=-3