ANSWER:
7/3 Ω
STEP-BY-STEP EXPLANATION:
We have that as it is a parallel circuit, the total resistance is calculated as follows:
[tex]\frac{1}{R_t}=\frac{1}{R_1}+\frac{1}{R_2}+\frac{1}{R_3}_{}_{}[/tex]Replacing:
[tex]\begin{gathered} \frac{1}{R_t}=\frac{1}{3}+\frac{1}{21}+\frac{1}{21} \\ \frac{1}{R_t}=\frac{7}{21}+\frac{1}{21}+\frac{1}{21} \\ \frac{1}{R_t}=\frac{9}{21} \\ R_t=\frac{21}{9}=\frac{7}{3}\Omega \end{gathered}[/tex]Total resistance is 7/3 Ω