Let's solve each equation step by step:

37x = 259
To solve for x, divide both sides by 37:
x = 259/37
x = 7

252/y = 21
To solve for y, multiply both sides by y and then divide by 21:
252 = 21y
y = 252/21
y = 12

z/18 = 6
To solve for z, multiply both sides by 18:
z = 6 * 18
z = 108

((23.79/7.8 - 6.8/17) 3.04 - 2.04) 0.85
First calculate the values inside the parentheses:
(3.05205128205 - 0.4) 3.04 - 2.04
(2.65205128205) 3.04 - 2.04
8.05691752526 - 2.04
6.01691752526

Finally, multiply by 0.85:
6.01691752526 * 0.85
5.11438089647

Therefore, the final result is 5.11438089647.