If you were to produce a 3 digit multiple of 7 that has a final digital sum of 7 using the formula; 7(1+9k). How do you calculate what k is?
If I understand the question correctly, we get several constraints from the conditions:
Dividing all parts by 7 we get
Subtracting 1 from all parts we get
Dividing all parts by 9 we get
All of these values of