## Elementary Algebra

$x=9$
Let the unknown number be $x$. Since, the sum of $x$ and two-thirds of $x$ is 15, we obtain: Step 1: $x+\frac{2}{3}x=15$ Step 2: $\frac{3x+2x}{3} =15$ Step 3: $\frac{5x}{3} =15$ Step 4: $5x=3(15)$ Step 5: $5x=45$ Step 6: $x=9$