If building a tower costs $100 for the first 10 feet and after that the cost of the labor goes up $25 per 10 feet, the next 10 feet are $125 and the next $150 etc. How much would it cost to build a 90-foot tower. I need to know which formula to use please

Question

If building a tower costs $100 for the first 10 feet and after that the cost of the labor goes up $25 per 10 feet, the next 10 feet are $125 and the next $150 etc.  How much would it cost to build a 90-foot tower.  I need to know which formula to use please

tad1 · Answer

9(100) + 8(25) +7(25) +6(25) + 5(25) +4(25) + 3 (25) +2(25) +25
=900 + 36(25)