The terms of the sequence can be written as : $u_r=ar+b$ in this case, being that they have a regular common difference for each of the r terms.

We can rewrite the sequence as $a+b,2a+b,3a+b,...$ where a is the common difference of the sequence and b is a given constant gotten by solving

$a+b=9$ or $2a+b=4$ or any other one.

The common difference here is 4 - 9 = -1 - 4 = -5.

$-5+b=9⟹b=9+5=14$

$\therefore$ The equation can be written as $u_r=-5r+14$.