x:45=28:20

To solve the proportion \( \frac{x}{45} = \frac{28}{20} \), you can cross-multiply:

\[ x \cdot 20 = 28 \cdot 45 \]

Now, calculate \( 28 \cdot 45 \):

\[ 28 \cdot 45 = 1260 \]

So, we have:

\[ 20x = 1260 \]

Now, divide both sides by 20 to isolate \( x \):

\[ x = \frac{1260}{20} \]

Calculating \( \frac{1260}{20} \):

\[ x = 63 \]

Thus, the solution is:

\[ x = 63 \]