Given is the adjoining circuit with
$R_1=5 ~\Omega$
$R_2=20 ~\Omega$
$R_3=10 ~\Omega$

1. determine the equivalent resistance $R_{\rm eq}$ between A and B by summing the resistances.

2. now let the voltage from A to B be: $U_{\rm AB}=U_0= 30 ~\rm V$. What is the current $I$?