Explanation
where x is the number of days since the start of the job
and f(x) is the rate of change
Step 1
a)find the total expenditure if the job takes 12 days
so, as x represents the number of days, just replace and calculate
let x= 12
so
a) 51.1
Step 2
now, let's find the total spent on the job from the 10 to 20th day
a) find the x value ( number of days since the job started)
x= 20 days-10dys= 10
so
x= 10
