x-21:8*5+7=22;x=?
x-9:7*4+8=20;x=?

[tex]x- \frac{21}{8} *5+7=22[/tex]
[tex] \frac{8x-49}{8} = \frac{22}{1} [/tex] ⇒[tex](8x-49)*1=8*22[/tex]
[tex] \frac{8x-49}{8x} = \frac{8*22}{8x} [/tex]
[tex] \frac{8*22}{8x} = \frac{22}{x} [/tex]
[tex] \frac{8x-49}{8x} = \frac{22}{x} [/tex]
[tex]1- \frac{49}{8x} = \frac{22}{x} [/tex]
[tex]- \frac{225}{8x} =-1[/tex]
[tex] \frac{8x-225}{8x} =0[/tex]
8x=225
x=[tex] \frac{225}{8} [/tex]
x=[tex]28 \frac{1}{8} [/tex]

[tex]x- \frac{9}{7} *4+8=20[/tex]
[tex] \frac{7x+20}{7} = \frac{20}{1} [/tex] ⇒[tex](7x+20)*1=7*20[/tex]
[tex] \frac{(7x+20)*1}{7x} [/tex] =[tex] \frac{7*20}{7x} [/tex]
[tex] \frac{7x+20}{7x} = \frac{7*20}{7x} [/tex]
[tex] \frac{7*20}{7x} = \frac{20}{x} [/tex]
[tex] \frac{7x+20}{7x} = \frac{20}{x} [/tex]
[tex] \frac{20}{7x} +1= \frac{20}{x} [/tex]
[tex] -\frac{120}{7x} =-1[/tex]
[tex] \frac{7x-120}{7x} =0[/tex]
7x=120
[tex]x= \frac{120}{7} [/tex]
x=[tex]17 \frac{1}{7} [/tex]