The equation is .
1/2 is equivalent to 4/8, and 2 1/8 is equal to 17/8. (two full sets of 8 + 1 = 8 + 8 + 1, or 17)
The new equation is . Subtract the numerators.
17 - 4 = 13 or 13/8
The improper fraction simplifies to
.
Hope this helps :)