you consider the arithmetic series with first term 30, common difference 1, and last term 80
the sum of arithmetic sequence is n/2(first term + last term), and there are (80-30)+1 = 51 numbers so n = 51 and so 51/2(30+80) = 2805 which represents the sum 30 + 31 + 31 + ... + 78 + 79 + 80
Say he mows 1 lawn every day, per week. He'd spend a total of $10.50 on gas and $7 for an advertisement for that week. Which would equal his total profit being $52.50 per week is his business.
