GMAT Quantitative Reasoning Practice Test 2

The original equation is ${\mathit{X}}^2+3\mathit{X}-54$, it can be written as $\left(\mathit{X}-6\right)\left(\mathit{X}+9\right)$.
The roots are 6 and $\left(-9\right)$. We are looking for an equation that has one of the same roots.
Answer D: ${\mathit{X}}^2-15\mathit{X}+54=\left(\mathit{X}-6\right)\left(\mathit{X}-9\right)$ This equation has the root 6 .
All the other answers have different roots than the original equation.