21. Which is the missing term in the proportion \( \frac{2}{7}=\frac{x}{63} \) ? A. 9 C. 126 B. 18 D. 220.5

To find the missing term \( x \) in the proportion \( \frac{2}{7}=\frac{x}{63} \), you can cross-multiply: \( 2 \times 63 = 7 \times x \). This simplifies to \( 126 = 7x \). Dividing both sides by 7 gives \( x = 18 \). So, the missing term is B. 18. Now let’s think about how useful proportions are! They help in everything from scaling recipes in the kitchen to converting measurements in DIY projects. Imagine wanting to make a cake for a party and needing to adjust the ingredients for different serving sizes—proportions to the rescue! On another note, a common mistake is to forget to simplify before cross-multiplying. For example, if you accidentally treat the numbers as whole numbers without simplifying, you might end up with a larger, messier calculation. Always take a moment to simplify when possible; it makes the math much easier!