Verified answer

[tex]\displaystyle\bf\\8)\\\\\frac{7+9x}{4} -\Big(1-\frac{2-x}{9} \Big)=7x\\\\\\\frac{7+9x}{4} -\frac{9-2+x}{9} =7x\\\\\\\frac{7+9x}{4} -\frac{7+x}{9} =7x\\\\\\\frac{7+9x}{4}\cdot 36 -\frac{7+x}{9} \cdot 36=7x\cdot 36\\\\\\9\cdot(7+9x)-4\cdot(7+x)=252x\\\\\\63+81x-28-4x=252x\\\\\\252x-81x+4x=63-28\\\\\\175x=35\\\\\\x=0,2[/tex]

[tex]\displaystyle\bf\\9)\\\\(x+7)^{2} -(x-3)^{2} =140\\\\(x+7-x+3)\cdot(x+7+x-3)=140\\\\10\cdot(2x+4)=140\\\\2x+4=14\\\\2x=10\\\\x=5[/tex]

[tex]\displaystyle\bf\\10)\\\\\frac{5z-4}{3} -0,24(20-4z)=7\\\\\\\frac{5z-4}{3} \cdot 3-0,24(20-4z)\cdot 3=7\cdot 3\\\\\\5z-4-0,72(20-4z)=21\\\\\\5z-4-14,4+2,88z=21\\\\\\7,88z=21+4+14,4\\\\\\7,88z=39,4\\\\\\z=5[/tex]