(1,8 + 1 2/7) : (1,8 - 1 2/7)

1. Convert decimals to fractions: (18/10 + 9/7) : (18/10 - 9/7) = (9/5 + 9/7) : (9/5 - 9/7).
2. Find common denominators and perform addition/subtraction: ((63+45)/35) : ((63-45)/35) = (108/35) : (18/35).
3. Divide the fractions: (108/35) * (35/18) = 108/18 = 6.