One number is 800 less than 3 times the other, and their sum is 1,200. find the numbers.

You can use variables to get the answer. So there's x, and the other number is 800 less than 3 times x

Their sum is 1,200, so you get this equation:

x + 3x - 800 = 1,200 (add like terms)
4x - 800 = 1,200 (add 800 on both sides)
4x = 2,000 (divide by 4 on each side)
x = 5,000

The first number is 5,000.
If the second number is 800 less than 3 times the other, 500(3) - 800 = 700.

CHECK YOUR WORK:
5,000 + 700 = 1,200
1,200 = 1,200

THE TWO NUMBERS ARE: 5,000 & 700