0.05n+0.03(1200-n)=42

Solution for 0.05n+0.03(1200-n)=42 equation:

Simplifying
0.05n + 0.03(1200 + -1n) = 42
0.05n + (1200 * 0.03 + -1n * 0.03) = 42
0.05n + (36 + -0.03n) = 42

Reorder the terms:
36 + 0.05n + -0.03n = 42

Combine like terms: 0.05n + -0.03n = 0.02n
36 + 0.02n = 42

Solving
36 + 0.02n = 42

Solving for variable 'n'.

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

Add '-36' to each side of the equation.
36 + -36 + 0.02n = 42 + -36

Combine like terms: 36 + -36 = 0
0 + 0.02n = 42 + -36
0.02n = 42 + -36

Combine like terms: 42 + -36 = 6
0.02n = 6

Divide each side by '0.02'.
n = 300

Simplifying
n = 300