a. $8x+(-3)=-4x+39 $
⇒ $8x+4x=39+3 $
⇒ $12x=42 $
⇒ $x=$$\frac{7}{2}$
Vậy S={$\frac{7}{2}$}
b. $11.107+11.18-25.11$
$=11.(107+18-25)$
$=11.100=1100$
c. $17.(15-16)+16.(17-20)$
$=17.15-17.16+16.17-16.20$
$=(-17.16+16.17)+(17.15-16.20)$
$=0-65=-65$
$153.177-153.77+100.(-77)$
$=153.(177-77)+100.(-77)$
$=153.100+100.(-77)$
$=100.(153-77)$
$=100.76=7600$