I will assume that "C=600 cm" refers to the radius of the given circle. Clearly, mABC refers to the length of arc ABC and is 75 cm.
The formula for arc length is s=r(angle in radians).
Here s=75 cm and r=600 cm. Thus, (angle in radians) = s/r, or
(angle) = 75 cm / 600 cm = 0.125 radian.
We must convert this to degrees.
0.125 radian * (180 degrees)/(3.14 rad) = 7.17 degrees = <ADC