To get an x³ in the answer:
--- Multiply the +1 from the first factor with the 2x³ of the second factor to get 2x³
--- Multiply the -8x times the -7x² to get 56x³
--- Multiply the -3x² times the 3x to get -9x³
--- Multiply the -3x³ times the 4 to get -12x³
Add these terms together to get the coefficient that you want ...
To get an x³ in the answer:
--- Multiply the +1 from the first factor with the 2x³ of the second factor to get 2x³
--- Multiply the -8x times the -7x² to get 56x³
--- Multiply the -3x² times the 3x to get -9x³
--- Multiply the -3x³ times the 4 to get -12x³
Add these terms together to get the coefficient that you want ...