How many equations in the same variables must be in a set to solve a system of linear equations?

For a unique solution, there must be as many consistent, independent equations as there are variables.

Step-by-step explanation:

Each equation lets you write an expression for one variable in terms of the others in that equation. That expression can be substituted throughout the system, reducing the number of equations and variables by one each.

After n-1 such substitutions in a system of n equations, there will be one equation left. If that is an equation in one variable, then the solution to the system can be easily found. If more than one variable remains (> n variables in n equations), then the system cannot be solved for definitive values of each of the variables.

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If the equations are inconsistent, there is no solution. If the equations are dependent, then there is no unique solution.