If a zero quotient is acceptable, then the answers are 4, 5, and 6.
If the quotient must be at least 1 to qualify for your instructor's
definition of 'divisible', then the answers are:
7 + 4 = 11,
8 + 5 = 13,
and 9 + 6 =15.


The relationship is:


 where N is the number (also referred to as the dividend),
Q is the quotient, D is the divisor, and R is the remainder.


So for your first example:  N is what we want to determine, Q is either 0 or 1
depending on what 'divisible' means, D is 7, and R is 4.  Hence:


 or 


I'll let you work out the other two.