Resistors of 5 ohms and 10 ohms are connected in series with a battery supplying 3 volts. What is the total resistance ? And calculate the current in the circuit.

For the first part of the question we note that the resistors are in series, this means we can simply add together the resistance, giving a value of:
15 ohms

For the second part we use the equation V=IR, 
substituting in the known voltage and calculated resistance:
3 = 15 * I
I = 3/15 = 0.2 Amps