math
posted by Taylor .
the annual household cost of telephone service in the US increased at a relatively constant rate of $27.80 per year from 1981 to 2001. IN 2001 the annual household cost of telephone service was $914.
a:What was the annual household cost of telephone service in 1981?
B: Write an equation that gives the annual household cost of telephone service as a function of the number of year since 1981.
C: find the household cost of telephone service in 2000

cost at t years from 1981 is
c = x + 27.80t
to find the cost in 1981, just plug in c=914 and t=20 and solve for x.
The function is above. It's kind of stupid to ask for the cost in 2000  we know it's $27.80 less than in 2001! Should have asked for some other year, to make use of the formula.