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.

x plus y equals 28. x equals 3 y.

Step-by-step explanation:

The equation can be written as

x+y=28

x=3y

x is already partially solved here, so you could substitute it into the first equation to solve for y.

3y+y=28

4y=28

y=7  We have y, so substitute that in the second equation to solve for x.

x=3(7)

x=21

We now know that x=21 and y=7

Substitute the values into the first equation:

21+7=28

28=28

So that system of equations is correct.

a

step-by-step explanation: