To find the values of I1 and I2, we can use Ohm's Law which states V = I*R, where V is the voltage, I is the current, and R is the resistance.

First, we need to calculate the total resistance of the circuit:

R_total = R1 + R2
R_total = 3 + 12
R_total = 15 Ohm

Now, we can calculate the total current flowing through the circuit using Ohm's Law:

I_total = V / R_total
I_total = 16 A

Now we can find the current flowing through each resistor:

I1 = $R2/R_{t}otal$ I_total
I1 = $12/15$ 16
I1 = 12.8 A

I2 = $R1/R_{t}otal$ I_total
I2 = $3/15$ 16
I2 = 3.2 A

Therefore, I1 = 12.8 A and I2 = 3.2 A.