the whining noise is probably your passenger whining about the stupid questions you ask
50 plus what = 850
900
850
750 rounded to the nearest 100 is 800
between 750-850
800! SIMP
1250
Normal just alittle problem with your engine or your fuel tank go to the Jiffy lube and ask them about it if you don't check the engine or fuel tank.
It means 750% change, I believe. A +100% change means that you add 100% of the original (or multiply by 2). So for a +750% change you multiply by 8.5 (750% + 100% = 850% --> multiply by 8.5)
$750-$850 in good condition.
750-850 non adjustable
There's no Volvo 850 2000. What you likely saw was a S70.