Answer
$x=18$ or $x=-3$.
Work Step by Step
By factorization, we have
$$x^2-15 x+54=(x+1)(x-2)=0.$$
Then we have
$$(x-18) =0, \quad \text{or} \quad (x+3)=0$$
that is $x=18$ or $x=-3$.
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.