Two or more elements in a circuit are in serial when the output of one of the element is the input of the next one.
In this position, the current that flows through these elements is the same, but the total voltage is the addition of the voltages in each element. Which it has to be the battery value for the voltage.(REMEMBER that this rule is only true in this kind of circuits) Vt = V1 + V2
To calculate the equivalent resistor, you have to do the addition of each serial resistor. Req = R1 + R2
In this case, the different elements of the circuits are positioned to have the same input and the same output. Wires in both sides are together, as you can see in the draw:
The equivalent resistor is calculated using this equation:
1/R = 1/R1 + 1/R2 + ...
At last, to calculate the resistance in mix circuits remember to calculate the total resistance in each piece of circuit.