How do you do this mentally step by step? : 73/4 - 1 2/7 - 3/2

You need to get rid of mixed numbers first of all. So that would make it 73/4 - 9/7 - 3/2
Then you need to get the LCD (least common denominator) which, in this case, is 28. You'd multiple each denominator and numerator by what it needs to become 28 in the denominator.
So 7×73/ 7x4 which is 511/28
And 4×9/ 4×7 which is 36/28
And finally 14×3/14×2 which is 42/28
You then subtract: 511-36-42 which is 433
Then put that answer over 28. So 433/28.
That is how i initially did it, so i hope that helps