Okay... I'm in some desperate need of help.

This word problem:

Part of $20,000 is invested at 12% interest. The rest is invested at 8% interest. The total interest from the two accounts os $1800. How much money was invested at each rate?

Im hella stumped... please help... sorry to bother you guys with something thats not very advanced...

Also, it would be nice to have the equation. Step by step, if I have the first one i feel i can figure the rest out. With explanations, please.