The function you're to evaluate is
... f(x) = 0.5x +3.40
Using function notation, the value for x = 2 is ...
... f(2)
For x = 3.5, the value is ...
... f(3.5)
and so on.
To actually evaluate the function, you need to put the value where x is in the function definition and do the arithmetic:
... f(2) = 0.5·2 + 3.40 = 1.00 +3.40 = 4.40
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The function gives the charge for a package based on its weight in ounces. The result of evaluating the function for the given weights is that you find the charges for delivery of those packages.