Answer:
![(4^(15) )/(b^(21) )](https://img.qammunity.org/2021/formulas/mathematics/high-school/f43h2ux5jud8sayc3t9il2o0tv4yc9ahzl.png)
Explanation:
First, multiply the exponent 7 and the -3 together, giving you:
![b^(-21)](https://img.qammunity.org/2021/formulas/mathematics/high-school/5eh4659p7pjg3ijffprij9ww4ygkpwxswy.png)
Then, multiply the exponent 5 and the -3 together, giving you:
![4^(-15)](https://img.qammunity.org/2021/formulas/mathematics/high-school/6u9cztywm0sjhi94jklwqr1u76l8rrrwu7.png)
But since you can't have a negative exponent, you need to switch the numbers in their places. This is because, when you have a negative exponent, you either switch it to under 1 or over 1, depending on where it currently is:
![(4^(15) )/(b^(21) )](https://img.qammunity.org/2021/formulas/mathematics/high-school/f43h2ux5jud8sayc3t9il2o0tv4yc9ahzl.png)