The answer is -4.5
To solve these types of problems it's best to work backwards.
-2 - 16 = -18
4 x (n) = -18
n = -18/4
n = -4.5
Check out -m-a-t-h-w-a-y-.-c-o-m- (This helps a lot!)
since triangles are similar
4/x = 7x/7
=》 4/x = x
=》x^2 = 4
=》 x = 2
for right triangles a^2 = b^2+c^2
DF^2 = 7^2+2^2 = 53
=》 DF = 7.28
perimeter of DEF = 7 +2+7.28 = 16.28
(0, 4) and (2, 0) are the coordinates