Ответ:

[tex] = {x}^{2} + 10x \times 25 - ( {x}^{2} - 25) + 15x - 25 = {x}^{2} + 25x - {x}^{2} + 25 = 25x + 25 \\ x = 1 \\ 25 \times 1 + 25 = 50[/tex]