Find the sum of all the multiples of 5 from 5 to 105

Multiples of 5 are 5, 10, 15, 20, etc.this is an arithmetic sequence with a common difference of 5.the sum of the terms in an arithmetic sequence is an an arithmetic series. the sum of an arithmetic series with  terms isif we have the first term  and the last term as  , with common difference  , then we can find the number of terms using the explicit rule.so using this with the sum formula,1155