Regarding investment, my suggestion (if you work in the US) is to open a basic (because it doesn’t periodically charge you fees) E*TRADE account here. They will provide an interface for buying and selling shares of stocks and various other things (ETFs and such; I mention stocks and ETFs because those are the only things I’ve tried doing anything with). They will charge you $10 for every transaction you make, so unless you’re going to be (or become) active/clever enough to make it worthwhile, it makes sense not to trade too frequently.
EDIT: These guys appear to charge less, though they also deal in fewer things (e.g. no bonds).
The way I’d try to do this problem mentally would be:
Relative to the desired concentration of 55%, each unit of 40% is missing .15 units of alcohol, and each unit of 85% has .3 extra units of alcohol. .15:.3=1:2, so to balance these out we need (amount of 40%):(amount of 85%)=2:1, i.e. we need twice as much 40% as 85%. Since we’re using 1kg of 40%, this means 0.5kg of 85%.