In the figure, the missing length is 20.1
How to find the required length
The missing length is solved using the formula
EG * EF = DE²
EG = EF + FG = 13 + 18 = 31
plugging in the values, we have
31 * 13 = DE²
DE² = 403
DE = √403
DE = 20.075
DE = 20.1