if 91z 5 is a multiple of 9 where z is a digit what might be the value of z?

Answer 1

Do you mean a 4-digit number 91z5?

The digits of any multiple of 9 add up to a multiple of 9.

So, 9+1+z+5 = 15+z
So, z=3 to make the sum 18.

9135 = 9*1015