Pre calculus 12 grade

Question

Please explain foe me one question: Your grandparents gave you a $500 gift during the holiday, that you deposited on a saving account. You plan to add $ 25 to the gift every week to save for summer break.

A) Which function represents the amount in account after each deposit as an arithmetic sequence, let , a1=500 : a(n)=500+25n , a(n)=500-25n, a(n)=25n+475 , a(n)=25n-475

I answered a(n)= 500+25n it incorrect answers. Correct answers is a(n)= 25n+475, I don not understand about it.

Answer 1

If a₁ = 500, then a₂ = 525, a₃ = 550, ...

The sequence is arithmetic with common difference d = 25 and a₁ = 500.

a_n = a₁ + (n - 1)d = 500 + 25(n - 1) = 25n + 475