To simplify this expression, we first need to find a common denominator for the fractions.

(5/6 - 3/10) = (25/30 - 9/30) = 16/30 = 8/15

(3/10 + 2/15) = (9/30 + 4/30) = 13/30

So, (5/6 - 3/10) / (3/10 + 2/15) = (8/15) / (13/30)

To divide by a fraction, we can multiply by the reciprocal:

(8/15) / (13/30) = (8/15) * (30/13) = 240/195 = 48/39 = 16/13

Therefore, (5/6 - 3/10) / (3/10 + 2/15) simplifies to 16/13.