#### Answer

$113$

#### Work Step by Step

Solve.$(7+8i)(7-8i)$
Need to drop the parentheses and multiply the terms and apply the formula of sum of two multiples such as: $(a+b)(a-b)=a^2-b^2$
$=(7)^2-(8i)^2$
Since, $i^2=-1$
Thus, $=49-64(-1)$
or,$=49+64$
or, $=113$