The slope is the relationship between the cost of the gym and how long you are there for. the y-intercept is how much it costs to go to the gym for no hours ie the start-up cost.
21.2264 is 21.2 rounded to the nearest tenths; the place after the decimal is there tenths place so in the hundreths place, the number 2 is less than 5 therefore rounding it to 2.
