First you should ask how you can express each side in terms of the smallest. Let the smallest side equal x. Because the second side is 6 more than the smallest, you can write it as x + 6. The third side is twice the size of the smallest, so you can call it 2x.
All of these sides add up to equal 25 units, so you can write the equation
x + x + 6 +2x = 25
From there, you can add like terms, solve for x, and plug it in to solve for the lengths of the other sides. Lmk if you have any more issues.
