$24.(16-5)-16.(24-5)$
$=24.16-24.5-16.24+16.5$
$=-24.5+26.5$
$=5.(-24+26)$
$=5.2$
$=10$
$29.(19-13)-19.(29-13)$
$=29.19-29.13-19.29+19.13$
$=-29.13+19.13$
$=13.(-29+19)$
$=13.10$
$=130$
$31.(-18)+31.(-81)-31$
$=-31.(18+81+1)$
$=-31.100$
$=-3100$
$(-12).47+(-12).52+(-12)$
$=-12.(47+52+1)$
$=-12.60$
$=720$
$13.(23+22)-3.(17+28)$
$=13.45-3.45$
$=45.(13-3)$
$=45.10$
$=450$
$-48+48.(-78)+48.-21$
$=-48.(1+78+21)$
$=-48.100$
$=-4800$