Answer
Fill the blanks with
$4x,$
$7$,
like
Work Step by Step
$(4x+7)(x^{2}+8x+3)$= ... distribute as $(A+B)C=AC+BC$
... multiply each term of $x^{2}+8x+3$ with each term of $(4x+7)$
... we start with $4x$
$=4x(x^{2}+8x+3) +...$ (unfinished)
... and then with $7$
$=4x(x^{2}+8x+3) +7(x^{2}+8x+3)$
... distribute each parentheses as $A(B+C+D)=AB+AC+AD$
$=4x^{3}+32x^{2}+12x+7x^{2}+56x+21$
... Now, combine like terms
$=4x^{3}+(32x^{2}+7x^{2})+(12x+56x)+21$
$=4x^{3}+39x^{2}+68x+21$
