Solve the Problem $V$ (In Volts) Through a 72 -Ohm Line to a Variable

Multiple Choice

Solve the problem.
-A voltage source of 12 volts can supply a voltage $V$ (in volts) through a 72 -ohm line to a variable resistance $R$ (in ohms) given by the following equation. $V=\frac{12 R}{72+R}$ . How fast does $V$ change with respect to $R$ when $R$ is 65 ohms?

A) $0.204 \mathrm{~V} / \Omega$
B) $0.167 \mathrm{~V} / \Omega$
C) $6.307 \mathrm{~V} / \Omega$
D) $0.046 \mathrm{~V} / \Omega$