Please show work for formulas used

Problem 2. On Juan's twenty-sixth birthday, he deposited $7,500 in a retirement account. Each year thereafter, he deposited $1,000 more than the previous year. Using a gradient series factor, determine how much was in the account immediately after his thirty-fifth deposit if a) b) The account earned annual compound interest of 5% The account earned annual compound interest of 6% Answer: a) $1,915,499 b) $2,236,254