18 - 3n + 2 = n + 20 - 4n

if we move all n's on one side and the numbers on the other side we get the equivalent equation

- 3n - n + 4n = 20 - 2 - 18

0 = 0 this means that for whatever n we take the equation 18 - 3n + 2 = n + 20 - 4n counts (its true)

The set of solutions is infinite and consists of all real and complex numbers.