How would you check your answer for this word problem?

Question

One number is three less than six times another. Their sum is 39. Find the numbers. I came up with 33 and 6 but how do I check my answers to be sure that's right?

Answer 1

Plug them back into the original equations that you used to get the answer.

Those equations are:

y = 6x - 3

x + y = 39,

33 and 6 both work in those.