Answer:
For each birdhouse built, the total cost increases by $3.50.
Step-by-step explanation:
Let's try some of the answers and see if they work.
The "initial cost" will be the cost when 0 birdhouses are built.
... f(0) = 3.5·0 +24 = 24 . . . . . clearly, not $3.50
Then increasing the number of birdhouses by 1, the cost is ...
... f(1) = 3.5·1 +24 = 27.5 . . . . . the cost has gone up (not down) by $3.50
Clearly the total cost to build 1 birdhouse is not $3.50. (It is $27.50.)
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Our exploration of the formula leads us to conclude ...
... For each birdhouse built, the total cost increases by $3.50.
