Given:
Moment of intertia of first disk = 1.0 kg.m²
Spinning counterclockwise at = 20.0 rad/s
Rotational intertia of second disk = 4.0 kg.m²
Spinning clockwise at 15.0 rad/s
Let's find the angular velocity of the two disk system.
To find the angular velocity, apply the formula for angular momentum conserve:

Rewrite the formula for angular velocity, w:

Where:
I₁ = 1.0 kg.m²
w₁ = 20.0 rad/s
I₂ = 4.0 kg.m²
w₂ = 15.0 rad/s
Input values into the equation and evaluate:

Therefore, the angular velocity for the two disk system is 8.0 rad/s clockwise.
ANSWER:
8.0 rad/s clockwise.