To simplify the expression, we first convert all mixed numbers to improper fractions:

5цел 3/8 = (5 8) + 3 = 43/8
18цел 1/2 = (18 2) + 1 = 37/2
7цел 5/24 = (7 24) + 5 = 173/24
16 цел 2/3 = (16 3) + 2 = 50/3

Now we substitute the improper fractions back into the expression and simplify:

(43/8 + 37/2 - 173/24) ÷ 50/3
= (526/24 + 444/24 - 173/24) ÷ 50/3
= (797/24) ÷ (50/3)
= (797/24) * (3/50)
= 2391 / 1200

Therefore, the simplified expression is 2391 / 1200.