Math homework help?!?

I'm having some trouble with some math homework. These are 2 of the examples. If you could break them down step by step that'd be so helpful. 1) A bacteria is being treated with an antibiotic. At 8am there are 6500 bacteria but by 4 pm, there are 275. Write an exponential function to model the bacteria x hours after 8am. How many bacteria will there be at 10 pm? 2) The average cost of a 3 bedroom house is 150000 and is increasing at a rate of 3.5%. The function R=150*times*10*to the power of*0.021x provides a model for the pattern of expected increase after x years. Find the time when the average would be 475000.