Step 1: Recall what the perimeter of a triangle is.

A perimeter is the sum of the sides.

Step 2: Assign a variable to the side since the length of the side is unknown.

Let x be the first side.

Step 3: Let 2 x be the second side since the second side is twice as long as the

first side

Step 4: Let 2 x-4 is the third side, since the third side is 4 cm short

Step 5: Write the expression and solve for x

Add the sides to get the perimeter

x + 2 x + 2 x - 4 = 76 => 5 x - 4 = 76 => 5 x = 80 => x = 16.

Therefore, the first side is 16 cm, the second side is 32 cm and the third side is 28cm.