The initial value is 309.35
It means that in the year 2010 (starting year) the population was 309,350,000 people or written another way "309.35 million". The second way is more short so probably the more preferred method.
To find the value 309.35, simply look at the table under the value t = 0.
The initial fee of $50 is essentially the y intercept because this is the value when x = 0 (x is the number of labor-hours). So b = 50.
The slope is m = 30 because each increase of 1 hour leads to the cost bumping up by 30 dollars. In other words, slope = rise/run = (change in cost)/(change in hours) = 30/1
So we plug m = 30 and b = 50 into the y = mx+b formula to get y = 30x+50
Replace y with f(x) to get f(x) = 30x+50
The linear function for the cost is f(x) = 30x+50
Note: Some books may use other letters (instead of x and f(x)), but the idea is still the same
Once you know the cost function, you replace x with 4.5 to find the amount it will cost to have a painter work for 4.5 hours.
f(x) = 30x+50
f(4.5) = 30*4.5+50
f(4.5) = 135+50
f(4.5) = 185
It will cost 185 dollars to have the painter work for 4.5 hours
