Answer
$28$ units
$56$ units
$42$ units
Work Step by Step
Let the shortest side of the triangle be $x$
Given,
Length of one side is twice the length of the shortest side
$y=2x$ Equation $(1)$
Length of the third side is $14$ more than the length of the shortest side.
$z = 14 +x$ Equation $(2)$
Perimeter of the triangle is $126$ units
$x+y+z=126$
$x+2x+14+x=126$
$4x=126-14$
$4x=112$
$x=28$ units
$y=2x$
$y=2(28)$
$y=56$ units
$z = 14 +x$
$z = 14 +28$
$z = 42$ units