2. –0,3t² + 8,1t + (2,9t – 0,7t²)

2. $$-0,3t^2 + 8,1t + (2,9t - 0,7t^2) = -0,3t^2 + 8,1t + 2,9t - 0,7t^2 = -t^2 + 11t$$

Ответ: $$-t^2 + 11t$$