Answer:    [C]:    " x³ + 8x² + 11x − 20 " .
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Step-by-step explanation:
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Given:      "  f(x) =  x² + 3x − 4 " ;   and
                 " g(x) =  x + 5  "  ;
Find:         "  f(x) ⋅ g(x) "  :
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     f(x) ⋅ g(x)  = 
      " (x² + 3x − 4) (x + 5) " ;
      ↔  " (x + 5) (x² + 3x − 4) " ;
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 <u>Note</u>:  " (a + b) (c + d + e)  =  ac + ad + ae + bc + bd + ae " ;
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  →  " (x + 5) (x² + 3x − 4) 
              =  (x * x²) + (x * 3x) + (x*-4) + (5*x²) + (5*3x) + (5*-4) " ;
              =  (x³) + (3x²)  + (-4x) + (5x²) + (15x) + (-20) ;
              =   x³  + 3x² − 4x + 5x² + 15x − 20 ; 
  →  Combine the "like terms" :
           + 3x² + 5x²  =  + 8x²  ; 
            − 4x + 15x   =  + 11 x ; 
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  → And rewrite: 
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         →   "  x³  +  8x²  +  11x  − 20 " ; 
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        →  which is:  Answer choice:  [C]:   " x³  +  8x²  +  11x  −  20 " .
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      Hope this helps!
         Best wishes!
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