Answer:
[tex]{ \rm{ {5b}^{4} \times {4b}^{3} }}[/tex]
• from laws of indices:
[tex] \hookrightarrow \: { \boxed{ \rm{ {rx}^{n} + {px}^{m} = (r \times p) {x}^{(n + m)} }}} \\ [/tex]
• substitute:
[tex]{ \rm{ {5b}^{4} \times {4b}^{3} = (5 \times 4) {b}^{(4 + 3)} }} \\ \\ = { \boxed{ \boxed{ \rm{ \: 20 {b}^{7} \: \: }}}}[/tex]
