This is what is considered an arithmetic sequence because the common difference between term is 4. So one way you could write each term is the first term minus the common difference times the number times one. So assuming that the first number in the sequence is 70, you can write the expression as
, where 70 is the first term, 4 is the common difference and n is the nth-numbered term. Simplify this expression and it is now,
. So you were close, but you can't necessarily add a specific term each time to find the next term in the sequence because it is decreasing