$V = R \times I \Rightarrow R = \frac{{12v}}{{1/5A}} = 8\Omega $$\frac{1}{R} = \frac{1}{{{R_1}}} + \frac{1}{{{R_2}}} \Rightarrow \frac{1}{8} = \frac{1}{{24}} + \frac{1}{x}$$\frac{1}{x} = \frac{1}{8} - \frac{1}{{24}} = \frac{{3 - 1}}{{24}} = \frac{2}{{24}} = \frac{1}{{12}}$${R_2} = 12\Omega $