1. The problem is to understand why the expression $5\left(\frac{3y}{5}\right)$ simplifies as it does. 2. The expression involves multiplication of a number by a fraction: $5 \times \frac{3y}{5}$. 3. Important rule: When multiplying a whole number by a fraction, multiply the numerator by the whole number and keep the denominator the same. 4. Applying this rule: $$5 \times \frac{3y}{5} = \frac{5 \times 3y}{5}$$ 5. Simplify the fraction by canceling the common factor 5 in numerator and denominator: $$\frac{5 \times 3y}{5} = 3y$$ 6. So, $5\left(\frac{3y}{5}\right)$ simplifies to $3y$ because the 5 in the numerator and denominator cancel each other out. This is why the expression suddenly becomes $3y$ after simplification.