Answer:
a. y = 6x +15
b. 15
Step-by-step explanation:
a.
The differences in the number of trees is 4-2 = 2, 6-4 = 2, and so on. The differences in the corresponding cost is 39-27 = 12, 51-39 = 12, and so on. That means adding 2 trees to the quantity adds 12 to the cost.
Working in reverse, we can subtract 2 trees from the quantity and subtract 12 from the cost. When we do that for the first table entry, we find 2-2 = 0 trees cost 27-12 = 15. The cost per tree is 12/2 = 6.
Now, we have the cost per tree, and the cost for 0 trees. This lets us write the cost function as ...
y = 6x +15 . . . . y = cost for x trees
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b.
The cost for 0 trees is 15, so that must be the shipping charge.
The shipping charge is 15.
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Additional comment
You can do this without thinking too much by using the formulas for 'm' and 'b' to write the cost function.
m = (y2 -y1)/(x2 -x1) = (39 -27)/(4 -2) = 12/2 = 6
b = y -mx = 27 -6(2) = 15
Then the equation is ...
y = mx +b
y = 6x +15
