\( \frac { 15 b ^ { 4 } a ^ { 7 } } { 3 b } = \square b a \)

To simplify the expression \( \frac{15 b^4 a^7}{3 b} \), you can first divide the coefficients and then simplify the powers of \( b \). Dividing the coefficients gives you \( \frac{15}{3} = 5 \). For the \( b \) terms, you have \( b^4 \) divided by \( b \), which simplifies to \( b^{4-1} = b^3 \). Therefore, the expression simplifies to \( 5 b^3 a^7 \). So, the complete equation is \( 5 b^3 a^7 \) in the square. Now, if we fill in the blank, it becomes \( \square = 5 b^3 a^7 \).