a)

$x+15=8\frac{1}{3}$

$x=8\frac{1}{3}-15$

$x=-\left(15-8\frac{2}{3}\right)$

$x=\left(-6\frac{2}{3}\right)$

b)

$12,4-x=20$

$12,4-20=x$

$-\left(20-12,4\right)=x$

$x=\left(-7,6\right)$

c)

$2x+5=15\frac{3}{4}$

$2x=15\frac{3}{4}-5$

$2x=10\frac{3}{4}$                                   $/:2$

$x=10\frac{3}{4}:2$

$x=\frac{43}{4}\cdot \frac{1}{2}$

$x=\frac{43}{8}$

$x=5\frac{3}{8}$

d)

$-3x=3\frac{3}{4}$                                         $/:\left(-3\right)$

$x=3\frac{3}{4}:\left(-3\right)$

$x=\left(3+\frac{3}{4}\right):\left(-3\right)$

$x=3:\left(-3\right)+\frac{3}{4}:\left(-3\right)$

$x=\left(-1\right)+\left(-\frac{1}{4}\right)$

$x=\left(-1\frac{1}{4}\right)$

e)

$2\left(3x-4\right)=10$

$6x-8=10$

$6x=10+8$

$6x=18$                         $/:6$

$x=3$

f)

$-3\left(5+2x\right)=15$

$-15-6x=15$

$-15-15=6x$

$-30=6x$                                   $/:6$

$x=\left(-5\right)$

g)

$4\left(x+3\right)-2=-6$

$4x+12-2=-6$

$4x+10=-6$

$4x=-6-10$

$4x=-16$                        $/:4$

$x=\left(-4\right)$

h)

$30-10\left(2-3x\right)=-50$

$30-20+30x=-50$

$10+30x=-50$

$30x=-50-10$

$30x=-60$                                $/:30$

$x=\left(-2\right)$