Problems solving some inequalities questions

a) $\displaystyle \frac{\2x+3}{3} \leq x-5$

I did this:

$\displaystyle \frac{\3(2x+3)}{3} \leq 3(x-5)$

$\displaystyle 6x+9 \leq 3x-15$

$\displaystyle 6x-3x \leq -15-9$

$\displaystyle 3x \leq -24$

$\displaystyle x \leq -8$

$\displaystyle (inf , -8]$

however the answer should be : $\displaystyle [18,inf)$

b) another one

$\displaystyle \frac{\ x+4}{2} \geq \frac{\ x-2}{4}$

$\displaystyle \frac{\2(x+4)}{2} \geq \frac{\2(x-2)}{2(4)} $

$\displaystyle 2x+8 \geq \frac{\2x-4}{8}$

$\displaystyle 8(2x+8) \geq \frac{\8(2x-4)}{8}$

$\displaystyle 16x+64 \geq 16x-32$

$\displaystyle 16x-16x \geq -64 -32$

$\displaystyle 0 \geq -96$

however the answer should be $\displaystyle [-10, inf)$

c) last one

$\displaystyle 3x \leq x+1 \leq x-1$

$\displaystyle 3x-1 \leq x \leq x-1-1$

don't know what to do after this step