y:3=720:9

To solve the proportion \( \frac{y}{3} = \frac{720}{9} \), you can cross-multiply:

\[ y \cdot 9 = 720 \cdot 3 \]

Calculating the right side:

\[ 720 \cdot 3 = 2160 \]

Now, your equation is:

\[ 9y = 2160 \]

To find \( y \), divide both sides by 9:

\[ y = \frac{2160}{9} \]

Now, calculate \( \frac{2160}{9} \):

\[ 2160 \div 9 = 240 \]

So, \( y = 240 \).