(2x + 6)(9x - 8) - (2x + 4)(9x - 1) = 18x2 - 16x + 54x - 48 - (18x2 - 2x + 36x - 4) = 18x2 + 38x - 48 - 18x2 - 34x + 4 = 4x - 44
При х = 7,5:
4 × 7.5 - 44 = 30 - 44 = -14
Ответ: -14