Show that (2, 1) is a solution of the system of equations.

x + 3y = 5,

y = –x + 3

Substitute (2, 1) into x + 3y = 5 to get
.
Simplify the equation to get
.
Substitute (2, 1) into y = –x + 3 to get
.
Simplify the equation to get
.