= -0.8c^2 - 4c - 0.7(10c+5) + 0.8c^2 + 10c - 4
= -0.8c^2 - 4c - 7c - 3.5 + 0.8c^2 + 10c - 4
= -11c - 3.5 - 4
= -11c - 7.5.