6=8.69*0.4+8.5*0.2+X*0.4

Solution for 6=8.69*0.4+8.5*0.2+X*0.4 equation:

Simplifying
6 = 8.69 * 0.4 + 8.5 * 0.2 + X * 0.4

Multiply 8.69 * 0.4
6 = 3.476 + 8.5 * 0.2 + X * 0.4

Multiply 8.5 * 0.2
6 = 3.476 + 1.7 + X * 0.4

Reorder the terms for easier multiplication:
6 = 3.476 + 1.7 + 0.4X

Combine like terms: 3.476 + 1.7 = 5.176
6 = 5.176 + 0.4X

Solving
6 = 5.176 + 0.4X

Solving for variable 'X'.

Move all terms containing X to the left, all other terms to the right.

Add '-0.4X' to each side of the equation.
6 + -0.4X = 5.176 + 0.4X + -0.4X

Combine like terms: 0.4X + -0.4X = 0.0
6 + -0.4X = 5.176 + 0.0
6 + -0.4X = 5.176

Add '-6' to each side of the equation.
6 + -6 + -0.4X = 5.176 + -6

Combine like terms: 6 + -6 = 0
0 + -0.4X = 5.176 + -6
-0.4X = 5.176 + -6

Combine like terms: 5.176 + -6 = -0.824
-0.4X = -0.824

Divide each side by '-0.4'.
X = 2.06

Simplifying
X = 2.06