Ответ:

x – y = 54

x² – y² = 648

y = x – 54

x² – (x – 54)² = 648

x² – x² + 108x – 2916 = 648

108x – 2916 = 648

108x = 648 + 2916

108x = 3564

x = 3564 : 108

x = 33

y = 33 – 54

y = -21

Проверка:

33 – (-21) = 33 + 21 = 54 ✓

33² – (-21)² = 1089 – 441 = 648 ✓