(9 - (-0.8))^2 - (-0.8)((-0.8) - 7)
(9.8)^2 - (-0.8)(-7.8)
(9.8)^2 - 6.24
96.04 - 6.24
89.8

So, the value of the expression (9-b)^2 - b(b-7) when b = -0.8 is 89.8.