Solve the Fraction Equation: Finding the Numerator in ?/15a = 5b/15a

To solve this problem, we will follow these steps:

• Step 1: Note that we are given two fractions $\frac{?}{15a}$ and $\frac{5b}{15a}$.
• Step 2: Observe that both fractions have the same denominator $15a$.
• Step 3: For these fractions to be equal, their numerators must also be equal. Thus, $? = 5b$.

Now, let's apply these steps:

By equating the numerators of $\frac{?}{15a} = \frac{5b}{15a}$, we directly find that the missing expression in the numerator, denoted as $?$, must be $5b$.

Therefore, the correct answer is $5b$.