[tex](800 - 240) \div x = 20 \\ 500 \div x = 20 \\ 560 = 20x \\ 20x = 560[/tex]

[tex] \: \: \: \: x = 28[/tex]

х=28

(800-240)/х =20

560/х=20

560=20х

20х=560 /:20

х=28