First find the value or (DEA)
For this you will have to use the Pythagorean theory,

C is mainly the hypotenuse,
Meaning you either want to find A or B,
Since the hypotenuse has two segments, both values are 10, then just add them together making it 20,
Then 16 will be A or B, in this case it will be A,
To find a you must first move A to the other side by doing the opposite,

Now plug in the values,



Now just find the square root of both factors,

The value of (DEA) is,

Now we want to find (d)
Since 12 is the value of the base, then divide it 2 to find (DE), after just repeat the whole process but with the value of hypotenuse 10 instead of 20 since we want to find the smaller triangle,

Now plug in the value



Now find the square root of both factors,


The value of (d) is (8)
Hope this helped
:D