$
\begin{array}{l}
a. \\
12 - 4x \le 36 + 2x \\
12 - 6x \le 36 \\
- 6x \le 24 \\
x \ge - 4 \\
\\
b. \\
\eqalign{\frac{{6 - 2x}}{5} \le \frac{{4 - x}}{4}} \\
4\left( {6 - 2x} \right) \le 5\left( {4 - x} \right) \\
24 - 8x \le 20 - 5x \\
- 3x \le - 4 \\
x \ge 1\frac{1}{3} \\
\\
c. \\
200 - (80 - x) > 4(x + 15) \\
200 - 80 + x > 4x + 60 \\
120 + x > 4x + 60 \\
- 3x > - 60 \\
x < 20 \\
\\
d. \\
60 - x^2 \ge 4x \\
- x^2 - 4x + 60 \ge 0 \\
{\rm{Gelijkheid:}} \\
- x^2 - 4x + 60 = 0 \\
x^2 + 4x - 60 = 0 \\
(x + 10)(x - 6) = 0 \\
x = - 10 \vee x = 6 \\
{\rm{Oplossing:}} \\
- 10 \le x \le 6 \\
\\
e. \\
x^3 < 80x - 2x^2 \\
x^3 + 2x^2 - 80x < 0 \\
{\rm{Gelijkheid:}} \\
x^3 + 2x^2 - 80x = 0 \\
x(x^2 + 2x - 80) = 0 \\
x(x + 10)(x - 8) = 0 \\
x = 0 \vee x = - 10 \vee x = 8 \\
{\rm{Oplossing:}} \\
x<-10\vee 0<x<8\\
\end{array}
$
