EXPLANATION
Given the equation:
-8.5x -3.5x = -78
Jason can check this answer subtituting 6.5 in given equation and checking if this is right:
-8.5(6.5) - 3.5(6.5) = -78 (Multiplying numbers)
-55.25 - 22.75 = -78 (Adding numbers)
-78 = -78 [They are same numbers, solution it right}