Step-by-Step?

c^2 = 5c      divide both sides by  'c'

c = 5

 

 

x^2 + 13x +42 = 0   Use Quadratic formula ...or factor it to

(x+7)(x+6) = 0     so x+7 = 0     means x= -7     x+6 = 0  means x can also = -6

 

 

x^2-4x-21   = 0    factors to  (x-7)(x+3) = 0     so x =  7 or -3