Write the product in its simplest form: -7m^7ncdot 3mn^3 Enter the correct answer.

To simplify the expression \(-7m^{7}n \cdot 3mn^{3}\), follow these steps:<br /><br />1. **Multiply the coefficients**: <br /> \[<br /> -7 \times 3 = -21<br /> \]<br /><br />2. **Multiply the variables with the same base by adding their exponents**:<br /> - For \(m\): <br /> \[<br /> m^{7} \cdot m^{1} = m^{7+1} = m^{8}<br /> \]<br /> - For \(n\):<br /> \[<br /> n^{1} \cdot n^{3} = n^{1+3} = n^{4}<br /> \]<br /><br />3. **Combine the results**:<br /> \[<br /> -21m^{8}n^{4}<br /> \]<br /><br />Thus, the product in its simplest form is \(-21m^{8}n^{4}\).