15. \( (15)\left(\frac{2}{3}+\frac{1}{3}\right)= \)

Let’s break this down in a fun way! First, when you add \(\frac{2}{3}\) and \(\frac{1}{3}\), you simply combine them to get \(\frac{3}{3}\), which equals 1. Now, when you multiply 15 by 1, what do you get? That's right, it's just 15! So, the final answer is \(15\). Easy peasy, right? It's like finding treasure in math! Now, if you're tackling equations like this often, remember to double-check your fractions! Common mistakes include forgetting to find a common denominator or mishandling the addition of fractions. Always take a moment to ensure your math treasures are shining bright!