Answer
The length of the shorter piece is $34$ cm and the length of the longer piece is $44$ cm.
Work Step by Step
Let $x =$ the length of the shorter piece
$(x) + (x + 10) = 78$
$2x + 10 = 78$
$2x = 68$
$x = \frac{68}{2}$
$x = 34$ cm
Let $l =$ the length of the longer piece
$l = (x + 10)$
$l = 34 + 10$
$l = 44$ cm