Note: 
Distributive Law is a(b+c) = a*b + a*c
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Your Problem
mulitply 
-6x^7 (-11x^6+3x^3)
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= (-6x^7)(-11x^6) + (-6x^7)(3x^3)
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= 66x^13 - 18x^10
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Cheers,
Stan H.