a person hired a firm to build a cb radio tower. the firm charges $100 for labor for the first 10 feet. after that the cost of the labor for each succeeding 10 feet is $25 more than the preceding 10 feet. that is, the next 10 feet will cost $125 the next 10 feet will cost $150 ect. how much will it cost to build a 90-foot tower? put it in a sequence
a = 100
d = 25
Tn = 100 + 25(n-1)
you want to add up 9 terms of this sequence:
S9 = 9/2 (2*100 + 8*25) = 1800