Question 1106233
This needs completing the square, since that would give one zero with multiplicity 2.  This is done by taking the coefficient of the x term, dividing it by 2 and squaring it.  That will give the coefficient of the constant.
Here, those values are:
[(1/2)(k-5)]^2=(4-5k)
(1/4)(k^2-10k+25)=(4-5k)
k^2-10k+25=16-20k, multiplying by 4
k^2+10k+9=0
(k+9)(k+1)=0
k=-9 and -1