In a parallel circuit, the equivalent resistance is the reciprocal of (the sum of the individual reciprocals).
1/R = 1/10 + 1/21 + 1/13
1/R = 0.225 mhos
R = 4.45 ohms
I = V / R
The total current out of the battery is
I = (9v)/(4.45ohms)
I = 2.02 Amperes
As the total current leaves the battery, it splits into 3 paths, and each resistor gets part of it. The 10ohm resistor gets the most current; the 21ohm resistor gets the least current. After flowing through the resistors, the 3 currents join and add up to 2.02 Amperes again, and the same current returns to the battery.
Each resistor has the same 9v of EMF across it.