We can make an algebra problem to solve this. There is a more "hands on" approach, but this is the quickest.
Let x be the first number and let x + 7 be the second number.
x + (x + 7) = 49 (Add the x's)
2x + 7 = 49 (Subtract 7 from both sides to eliminate it from the left)
2x = 42 (divide both sides by 2 to leave x)
x = 21 This will be your first number. Now add 7.
x + 7 = 28 This will be your second number.
Check it:
21 + 28 = 49. Yes!