First group the coefficients and variables.

(– 8s³)(– 3s⁴) = (– 8 · – 3) (s³ · s⁴)

=  (24) (s³ · s⁴)            (Multiply:  – 8 · – 3 = 24)

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

=  (24) (s^{3 + 4} )    

=  24s⁷                        (Add exponents: 3 + 4 = 7)

Product of  Product of (– 8s³)(– 3s⁴) is 24s⁷.