( -31/21х+5/7)-1/3=-2,4/7

(-31/21х)+(5/7)-(1/3)=-18/7

(-31/21х)-(1/3)+(5/7)=-18/7

-31/21х=(-18/7)+(1/3)-(5/7)

-31/21х=(-54/21)+(7/21)-(15/21)

-31/21х=-62/21

х=-62/21 : (-32/21)

х=-62/21 * (-21/31)

х=2