The sum of two numbers is 28. The first number, x, is three times the second number, y.

Which system of equations can be used to find the two numbers?

A system of equations. x plus y equals 28. x equals 3 plus y.
A system of equations. x y equals 28. x equals 3 y.
A system of equations. x y equals 28. x equals 3 plus y.
A system of equations. x plus y equals 28. x equals 3 y.