`4O + 5O_2 ----t^o----> 2P_2O_5`

`P_2O_5 + 3H_2O ---t^o----> 2H_3PO_4`

`=>` `B`

`x^2 + 5x - 6 = 0`

`x = (-5 ± 7)/2`

`<=> x = {-1; 6}`

PTHH:

`CuO + H_2t^o -> Cu + H_2O`

`m_(Ct) = (200.15%) + (300.25%) = 105g`

`m_(dd) = 200 + 300 = 500g`

`C% = 105/500 . 100% = 21%`

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