1) Make sure that the fractions (1/3 and 3/4) have a common denominator. Therefore, find the least common denominator (LCD).
After finding out the LCD, you should get 12.
2) Make the fraction 1/3 have an equivalent fraction where 12 is the denominator. To do so, since we know that 3 times 4 = 12, we should also do 1 times 4 = 4. Therefore, we now have the whole fraction as 26 1/4. Do the same thing to 3/4, but this time 4 times 3 = 12 so 3 times 3 = 9. This fraction will now be 17 9/12.
3) Try to subtract the fractions first. Since 4/12 is less than 9/12, we have to "borrow" a whole from 26 to make sure that 4/12 becomes a greater fraction than 9/12 so that we can easily subtract. Since we borrowed a whole, which in this case is worth 12 units (look at the fraction's denominator), we should add 12 to 4 to now get the numerator of 16. So we now have the top fraction being 25 16/12. Now we can actually subtract!
4) Do the fractions first, 16 - 9 = 7, to now get 7/12 and the whole numbers 25 - 17 = 8.
5) Our answer is now 8 7/12.
You can check the image below to see the work being done in accordance to the steps that I provided above.