z⁷ · 8z⁴ =   z⁷ · 8 · z⁴

=  8 · z⁷ · z⁴        (Apply commutative property of multiplication: a × b = b × a)

Since base is common,apply the product of powers property: a^m·aⁿ= a^{m + n}.

=  8 · z^{7 + 4}

=  8z¹¹                (Add exponents: 7 + 4 = 11) \ \

The product of  z⁷ · 8z⁴ is 8z¹¹.