(43 7/43+x)-31 8/43=19 42/43
(43⁷/₄₃+x)-31⁸/₄₃=19⁴²/₄₃ 43⁷/₄₃+x =19⁴²/₄₃ + 31⁸/₄₃ 43⁷/₄₃+x =50⁵⁰/₄₃ 43⁷/₄₃+x =51⁷/₄₃ x =51⁷/₄₃ - 43⁷/₄₃ x = 8
благодарен