Question 701571
Assume you mean {{{x^2+3*x+j=0}}}.   Either know what is the discriminant, or try filling in solution to quadratic equation.

{{{x=(-3+-sqrt(9-4*j))/2}}}

Notice if you want only Real solutions, then the square root's radicand must be positive.  {{{9-4*j>=0}}}.   Only a simple matter to find j.  

-4j>=-9
j<=(9/4)  [multiplied both sides by -(1/4)]