We know that the circuit is connected in series. In this kind of circuits the equivalent resistance is:
[tex]R_{eq}=R_1+R_2[/tex]
We also know that the total voltage in the circuit is equal to the sum of the voltage in each resistor, then:
[tex]V=V_1+V_2[/tex]
From this two things we know that:
Now, using the relation:
[tex]R=\frac{V}{i}[/tex]
We can calculate the current in resistor one:
[tex]\begin{gathered} 6=\frac{30}{i} \\ i=\frac{30}{6} \\ i=5 \end{gathered}[/tex]
