In the triangle above, if t=7, what is the value of r

Im not that good with division but i think 5 is -6but dont quote me on thatim not the best in division but thats my answer

This is what i found “an explicit formula designates the nth term of the sequence, as an expression of n (where n = the term's location). it defines the sequence as a formula in terms of n. this example is an arithmetic sequence(the same number, 5, is added to each term to get to the next term).” i hope this you for what your looking for. can you plz mark me brainliest?