Пошаговое объяснение:

[tex](120 + x) = 100\% \\ 120 + x = \frac{100}{100} \\ 120 + x = 1 \\ x = 1 - 120 \\ x = - 119 \\ \\ 12 + x = 20\% \\ 12 + x = \frac{20}{100} \\ 12 + x = \frac{1}{5} \\ x = \frac{1}{5} - 12 \\ x = - \frac{59}{5} . \: \: x = - 11 \frac{4}{5} [/tex]