.50(9.0-y)+.20y=3.30

Solution for .50(9.0-y)+.20y=3.30 equation:

Simplifying
0.50(9.0 + -1y) + 0.20y = 3.30
(9.0 * 0.50 + -1y * 0.50) + 0.20y = 3.30
(4.5 + -0.5y) + 0.20y = 3.30

Combine like terms: -0.5y + 0.20y = -0.3y
4.5 + -0.3y = 3.30

Solving
4.5 + -0.3y = 3.30

Solving for variable 'y'.

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

Add '-4.5' to each side of the equation.
4.5 + -4.5 + -0.3y = 3.30 + -4.5

Combine like terms: 4.5 + -4.5 = 0.0
0.0 + -0.3y = 3.30 + -4.5
-0.3y = 3.30 + -4.5

Combine like terms: 3.30 + -4.5 = -1.2
-0.3y = -1.2

Divide each side by '-0.3'.
y = 4

Simplifying
y = 4