All you have to do is take the length of the full line (13.8 cm) and subtract it by the first part (6.5 cm). Doing this gets you the final length of DE with is 7.3 cm.
In order to do this equation, your first step is to use the Order of Operations, or PEMDAS, which means that you multiply (M) two times two first before subtracting the equation (S). 2 times 2 is 4. 4 - 1 = 3. Hope I helped! :)
