Answer:
[tex] {b}^{28} [/tex]
Step-by-step explanation:
[tex] { \bigg( \frac{ {b}^{19} }{ {b}^{12} } } \bigg)^{4} \\ \\ = { \bigg( { {b}^{19 - 12} }} \bigg)^{4} \\ \\ = { \bigg( { {b}^{7} }} \bigg)^{4} \\ \\ = {b}^{7 \times 4} \\ \\ = {b}^{28} [/tex]
