#### Answer

$x=6cm$

#### Work Step by Step

Set up an equation that satisfies all three sides.
$2(2x)+x=30$
Factor out the expression (x) and add.
$5x=30$
Solve for x by dividing by 5.
$x=6$
Do a mental check by making sure that the value satisfies the problem.
$x=6$, and therefore $2x=12;2(12)+6=30$