The NOK angle is 120 °, the OD-ray traced inside it. How many degrees does the DOK angle contain

The NOK angle is 120 °, the OD-ray traced inside it. How many degrees does the DOK angle contain if the degree measure of the NOD angle is 20 ° greater than the degree measure of the DOK angle?

Based on these conditions, we will compose a system of two equations:
NOK = NOD + DOK.
NOD = DOK + 20º.
Then, substituting the second equation into the first, we find DOK:
NOK = NOD + DOK = DOK + 20º + DOK = 2 * DOK + 20º.
120º = 2 * DOK + 20º.
DOK = 50º.
The DOK angle contains 50º.