.90x+.05(18-x)=.10(-42)

Solution for .90x+.05(18-x)=.10(-42) equation:

Simplifying
0.90x + 0.05(18 + -1x) = 0.10(-42)
0.90x + (18 * 0.05 + -1x * 0.05) = 0.10(-42)
0.90x + (0.9 + -0.05x) = 0.10(-42)

Reorder the terms:
0.9 + 0.90x + -0.05x = 0.10(-42)

Combine like terms: 0.90x + -0.05x = 0.85x
0.9 + 0.85x = 0.10(-42)

Multiply 0.10 * -42
0.9 + 0.85x = -4.2

Solving
0.9 + 0.85x = -4.2

Solving for variable 'x'.

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

Add '-0.9' to each side of the equation.
0.9 + -0.9 + 0.85x = -4.2 + -0.9

Combine like terms: 0.9 + -0.9 = 0.0
0.0 + 0.85x = -4.2 + -0.9
0.85x = -4.2 + -0.9

Combine like terms: -4.2 + -0.9 = -5.1
0.85x = -5.1

Divide each side by '0.85'.
x = -6

Simplifying
x = -6