Answer
For $r$ near $5$ ,
$$
f(r) \approx 5^{2}+2(5)(r-5)=25+10(r-5)
$$
For $r$ near $10$ ,
$$
f(r) \approx 10^{2}+2(10)(r-10)=100+20(r-10)
$$
Work Step by Step
For $r$ near $5$ ,
$$
f(r) \approx 5^{2}+2(5)(r-5)=25+10(r-5)
$$
For $r$ near $10$ ,
$$
f(r) \approx 10^{2}+2(10)(r-10)=100+20(r-10)
$$
