Final answer:
To find the cost of mailing a first-class letter that weighs 4.2 ounces according to the given function f(w) = 0.49 + 0.21(w - 1), substitute the weight value w = 4.2 into the function and evaluate.
Step-by-step explanation:
To find the cost of mailing a first-class letter that weighs 4.2 ounces according to the given function f(w) = 0.49 + 0.21(w - 1), we need to substitute the weight value w = 4.2 into the function.
f(4.2) = 0.49 + 0.21(4.2 - 1) = 0.49 + 0.21(3.2) = 0.49 + 0.672 = 1.162
So, the cost of mailing a first-class letter that weighs 4.2 ounces according to the given function is $1.162.