Let x be the number.
"When 2/3 is added to a certain number" so we get x + 2/3
"The sum is 3 greater than twice that number" so it's 3 + 2x
So 2/3 + x = 3 + 2x
Subtract 2/3 from both sides:
2/3 + x = 3 + 2x
2/3 - 2/3 + x = 3 - 2/3 + 2x
x = 7/3 + 2x
Subtract 2x from both sides
x - 2x = 7/3 + 2x - 2x
-x = 7/3
Multiply by (-1) to get the positive x
-x = 7/3
x = -7/3
Hope this helps! :D