First we distribute the terms inside the parentheses:

5/8 2x - 5/8 y - 1/4 x - 3/8 y

Now we simplify each term:

10/8x - 5/8y - 1/4x - 3/8y

Combine like terms by adding or subtracting coefficients:

10/8x - 1/4x - 5/8y - 3/8y
(10/8 - 1/4)x - (5/8 + 3/8)y
(5/4 - 1/4)x - (8/8)y
4/4x - 1/2y
x - 1/2y

Therefore, 5/8(2x-y)-(1/4x+3/8y) simplifies to x - 1/2y.