You can work this out with basic maths in both directions given what we know using two well known sayings. Substitute Virgins or Chocolate as desired for your own versions.
if we use the saying
"True virtue makes dull company. Add whiskey."
true+variation=magnetic+deviation=compass
The plus signs are used for westerly changes ("add whiskey" = add westerly) If the variation or the deviation are EASTERLY, then use a minus sign.
We know the following
true = 172 (Nobody disputes this 180 minus 8 degrees drift)
variation = x (to be calculated)
magnetic = y ( to be calculated)
deviation = -2
compass = 195
we know variation and deviation are westerly so we add.
172 + x = y (magnetic)
y + (-2) = 195 (compass)
y must equal 197 as we know that 197 - 2 = 195
therefore 172 + x must equal 197
therefore 197 - 172 = x
therefore x (variation) = 25
therefore Answer = B
If we now do the reverse calculation using the saying
"Can dead men vote twice at elections?"
compass+deviation=magnetic+variation=true
The plus sign is used for easterly changes ("at elections." = add easterly) If the variation or the deviation are WESTERLY, then use a minus sign.
Again we know the following
true = 172
variation = x (to be calculated)
magnetic = y ( to be calculated)
deviation = -2
compass = 195
we know variation and deviation are westerly so we subtract.
195 - (-2) = y (minus minus 2 = plus 2)
therefore y (magnetic) = 197
197 - x (variation) = 172 (true)
therefore x (variation) = 25 (as 197 - 25 = 172)
Variation = 25
so I still think the answer is B
Regards
EddieHeli