Respuesta :

x +12 -sqrt(x) = 42

-sqrt(x) = -x+30

-sqrt(x)^2 = (-x+30)^2

x^2 - 61x + 900 = 0

(x-36) (x-25) = 0

 x = 36

36+12 = 48 - sqrt(36) = 48-6 = 42

 X  = 36