Answer
$40a^{2}+59a+21$
Work Step by Step
To find the product of $(5a+3)$ and $(8a+7)$, we need to use the distributive property in which each term of the first polynomial is multiplied to each term of the second polynomial:
$(5a+3)(8a+7)$
=$5a(8a+7)+3(8a+7)$
=$40a^{2}+35a+24a+21$
=$40a^{2}+59a+21$
