1. The problem is to solve the proportion $129.5:9 = x:50$ for $x$. 2. Recall that in a proportion $a:b = c:d$, the cross products are equal, so $a \times d = b \times c$. 3. Applying this rule, we have: $$129.5 \times 50 = 9 \times x$$ 4. Calculate the left side: $$129.5 \times 50 = 6475$$ 5. So the equation becomes: $$6475 = 9x$$ 6. To solve for $x$, divide both sides by 9: $$x = \frac{6475}{9}$$ 7. Show the cancellation step: $$x = \frac{\cancel{6475}}{\cancel{9}}$$ (no common factors to cancel, so this is just to show division) 8. Calculate the division: $$x \approx 719.444...$$ 9. Therefore, the value of $x$ is approximately $719.44$.