Find the value of the expression: - 0.5 (7b-12a) - (8.4a-14b) if a=-10; b=-6.

Replace a and b in the equation with their values given:

-0.5 (7 (-6) - 12 (-10) - (8.4 (-10) - 14 (-6))

Multiply within the parentheses

-0.5 (-42 + 120) - (-84 + 84)

Add inside the parenthesis:

-0.5 (78) - 0

Multiply:

-.05 x 78 = - 39

The answer is - 39