Xavier exercises by riding his bike. during his first week of training, he rides a total of 15 miles. each week he increases the number of miles biked by 0.4 miles. how many total weeks will it take xavier to first bike more than 500 miles total?

So he rides his bike 15miles the first week
he increases every week by 0.4 from the previous one
namely, an arithmetic sequence, whose first term's value is 15
what would be the term whose value is over 500?  well, we dunno

but we know it has to be 500 thereabouts, 500 or higher.... so.. hmmm let's take a peek, first term's value is 15, "common difference" is 0.4