To find out what happens when (2,1) is substituted into the equation x + 3y = 5, we simply need to replace x with 2 and y with 1, and then solve for the left-hand side of the equation.
Therefore, substituting (2,1) into the equation x + 3y = 5 we get:
2 + 3(1) = 5
Simplifying the left-hand side of the equation, we get:
2 + 3 = 5
Therefore, the left-hand side of the equation equals the right-hand side of the equation.