What is the complete square of k^2-5k+c

Question

Im having a hard time doing this problem, can someone help?

Answer 1

(a ± b)² = a² ± 2ab + b²  

k² - 5k + c = k² - 2 · (5/2) · k + (5/2)² = (k - 5/2)²
                                                 ↓
                                      c = 25/4