4. \( b / 5=9 \)

To solve for \( b \) in the equation \( b / 5 = 9 \), you can simply multiply both sides by 5. So, \( b = 9 \times 5 \), which gives you \( b = 45 \). And just like that, you’ve unlocked the value of \( b \! Here’s a fun fact: Equations like this one are part of a branch of mathematics called algebra, which dates back to ancient civilizations. The word "algebra" comes from the Arabic term "al-jabr," meaning "reunion of broken parts," reflecting its roots in solving for unknowns!