Can someone please answer this scientific notation question or explain it for me?

Ahigh definition tv cost $800 with a down payment of 2/5 of the cost. how much is left to pay, in dollars after the down payment has been made?

The following frequency table relates the weekly sales of bicycles at a given store over a 42-week period. value01234567frequency367108521(a) in how many weeks were at least 2 bikes sold? (b) in how many weeks were at least 5 bikes sold? (c) in how many weeks were an even number of bikes sold?

Iwill give ! if m∠a=59 and m∠3=81°, what is m∠b? m∠b= _[blank]_°