3.
$\frac{x-3}{x+2}$ =$\frac{3}{4}$
=>(x-3)×4=(x+2)×3
=>4x-12=3x+6
=>4x-3x=12+6
=>(4-3)x=18
=>1x=18
=>x=18
Vậy x=18
4.
$2^{x+2}$ - $2^{x}$ =96
=> $2^{x}$×4- $2^{x}$×1 =96
=>$2^{x}$×(4-1)=96
=>$2^{x}$×3=96
=>$2^{x}$=96÷3
=>$2^{x}$=32
=>$2^{x}$=$2^{5}$
=>x=5
Vậy x=5