The CAS Registry Mumber 6990-74-5 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 6,9,9 and 0 respectively; the second part has 2 digits, 7 and 4 respectively. Calculate Digit Verification of CAS Registry Number 6990-74: (6*6)+(5*9)+(4*9)+(3*0)+(2*7)+(1*4)=135 135 % 10 = 5 So 6990-74-5 is a valid CAS Registry Number.