Answer
The longer piece of the pipe is $48$ cm long and the shorter piece of the pipe is $42$ cm long.
Work Step by Step
Let $x = $ the longer length of the pipe
$(x) + (x - 6) = 90$
$2x - 6 = 90$
$2x = 96$
$x = \frac{96}{2}$
$x = 48$ cm
Let $y = $ the shorter length of the pipe
$y = (x- 6)$
$y = 48 - 6$
$y = 42$ cm