OBM 1985 Problem 1

$a, b, c, d$ are integers with $ad \ne bc$ . Show that $1/((ax+b)(cx+d))$ can be written in the form $r/(ax+b) + s/(cx+d)$ . Find the sum $1/1\cdot 4 + 1/4\cdot 7 + 1/7\cdot 10 + ... + 1/2998 \cdot 3001$ .