First, let's calculate the equivalent resistance of the three parallel resistors, using the formula below:
[tex]\begin{gathered} \frac{1}{R_{eq}}=\frac{1}{R_1}+\frac{1}{R_2}+\frac{1}{R_3}\\ \\ \frac{1}{R_{eq}}=\frac{1}{3}+\frac{1}{3}+\frac{1}{3}\\ \\ \frac{1}{R_{eq}}=1\\ \\ R_{eq}=1\text{ ohm} \end{gathered}[/tex]Now, let's add this resistance with the one resistance in series:
[tex]\begin{gathered} R_=R_{eq}+R_4\\ \\ R=1+3\\ \\ R=4\text{ ohms} \end{gathered}[/tex]To find the total current, let's divide the voltage by the total resistance:
[tex]\begin{gathered} I=\frac{V}{R}\\ \\ I=\frac{12}{4}\\ \\ I=3\text{ A} \end{gathered}[/tex]Therefore the correct option is b.
