Final answer:
After combining like terms and solving the equation -2.9x + 10 = 70, the value of x is found to be -20.69, which does not match the given options. There may be a typo in the original equation.
The correct answer is none of all.
Step-by-step explanation:
To solve the equation 2.8x + 10 - 5.7x = 70, we must first combine like terms. This gives us -2.9x + 10 = 70. Next, we subtract 10 from both sides, resulting in -2.9x = 60. Finally, we divide both sides by -2.9 to find the value of x, which gives us x = -20.69.
However, looking at the options provided (a. x = 6, b. x = 7, c. x = 8), none of them match the solution. It's possible there might have been a typo in the original equation. Please double-check the equation and try solving it again or provide the correct one.