4r⁵· 2r =  4 · r⁵ · 2 · r

= 4 · 2 · r⁵ · r       (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}.

= 4 · 2 · r^{5 + 1}

= 4 · 2 · r⁶            (Add exponents: 5 + 1 = 6)

= 8r⁶                     (Multiply: 4 × 2 =  8)

The product of  4r⁵· 2r is 8r⁶.