Question 564939
Distribute the k:
k(k-3)=28
k*k-k*3=28
k^2-3k=28
Subtract 28:
k^2-3k-28=0
Factor:
(k-7)(k+4)=0
Since the product of two expressions is zero for some k, one of them must be zero.  This implies:
k-7=0  OR  k+4=0
This implies:
k=7  OR  k=-4