In a certain code language, 'GOOD' is written as '75' and 'FINE' is written as '82'. How will 'BEST' be written in that language?

Let's find the relationship using the standard positional values (A=1, B=2, ..., Z=26) or reverse values (A=26, B=25, ..., Z=1).
Let's check the sum of opposite positional values for 'GOOD':

G → T (20)

O → L (12)

O → L (12)

D → W (23)
Sum of opposite values = 20+12+12+23=67.
To get 75: 67+8=75. (Note: 8=2×4 letters).

Let's check 'FINE' with the same logic:

F → U (21)

I → R (18)

N → M (13)

E → V (22)
Sum of opposite values = 21+18+13+22=74.
To get 82: 74+8=82.

The logic is: (Sum of reverse positional values) + 8.

Let's apply this to 'BEST':

B → Y (25)

E → V (22)

S → H (8)

T → G (7)
Sum of opposite values = 25+22+8+7=62.
Total value = 62+8=70.