Writing a "word sentence" into a "number sentence" part of the problem is sometimes the most difficult for a student to write.
"The Difference Between" means that you will subtract the next two things in the problem...so where it says "The difference between "2/3 of a number and 1/6 of the same number"...you put a minus sign where the "and" is.
When a word problem tells you that you are going to write "a number," you will write a letter (also known as a variable). So where the problem says, "The difference between 2/3 of 'a number'"...you write a letter like 2/3 x.
Putting the whole problem together...word for word, number for number, symbol for symbol...you get the following.
(I write out the "number sentence" above the "word sentence" so I can see that I remembered everything).
2/3 x - 1/6 x = 75
Difference between two-thirds of a number and one-sixth of the same number is 75. What is the number?