Respuesta :

dwh2o13
[tex] 5c^{7}( 5c^{8}) = 25 c^{15} [/tex]  you add the exponents when multiplying exponential factors with the same base:  

Really, your multiplying 4 factors.   Here is a different way to look at it:

5(5)(c⁷)(c⁸) = 25c¹⁵