The resistors R1 and R2 are connected in parallel across the voltage source of 10 V. There is a current that flows through both the resistors as a result of this. The two differ as the voltage source and the resistors are in parallel.
The current flowing through R2 due to the applied voltage is 10 mA. The current flowing through R1 is given by the formula V = I*R where V is the voltage applied across the resistor with resistance R and I is the current that flows through it as a result.
10 = 5*10^3*I
=> I = 2 mA
This gives the total current flowing through the circuit as 12 mA.