A tautology will have an infinite number of solutions, as it is true for all possible values of the variable by definition.
Example: 3(x+2) = 3x+6
All other linear equations in one variable will have one solution, which may include values that are undefined or indeterminate.
Examples:
... 3x-2 = 7 . . . solution is x=3
... x = 0/0 . . . . solution is an indeterminate number
... x = 1/0 . . . . solution is undefined
