Answer
Connect four 40-ohm resistors in parallel.
Work Step by Step
The equation is not given in this textbook, but for 4 resistors in parallel, the following relation holds.
$$\frac{1}{R_{parallel}} = \frac{1}{R_{1}} + \frac{1}{R_{2}} + \frac{1}{R_{3}} + \frac{1}{R_{4}} $$
Apply the equation to this problem.
$$\frac{1}{R_{parallel}} = 4 \times \frac{1}{40 \Omega} = \frac{1}{10 \Omega} $$
$$R_{parallel} = 10 \Omega$$
