I'm not saying the OP should ball park it for his PPL studies but once in the real world just divide it up into multiples of 6.
90 kts=1.5 nm minute
96kts=1.6 nm minute
102kts= 1.7nm minute etc.
98 kts is nearest to 96 so just multiply 1.6 by 2.5 which equals 4.0. If you're feeling particularly anal bung a bit on for the wife and kids.
Piperboy: you don't have it wrong, I use the same method. It's just the sine of the wind angle. 60 degrees off would actually be 0.866 but it's near enough to one for me. I use the same method for xwind component on takeoff/landing, which is what your drift angle is anyway.
Some the answers / remarks given here fall in to the category of RTFQ, were does the wind come in to the calculation ?
Come on, wouldn't be Prune without people jumping in at the deep end!