Ответ:

d=-1.1

Объяснение:

[tex]s14 = \frac{2 \times 7.1 + d(14 - 1)}{2} \times 14 = - 0.7[/tex]

[tex]( 14.2 +13 d) \times 7 = - 0.7 \\ 1.2 + 13d = - \frac{0.7}{7} \\14.2 + 13d = - 0.1 \\ 13d = - 0.1 - 14.2 \\ 13d = - 14.3 \\ d = - \frac{14.3}{13} \\ d = -1.1[/tex]