Which is a stretch of an exponential decay function?

f(x) = Four-fifths (five-fourths) Superscript x
f(x) = Four-fifths (four-fifths) Superscript x
f(x) = Five-fourths (four-fifths) Superscript x
f(x) = Five-fourths (five-fourths) Superscript x

Kayla wants to find the width, ab, of a river. she walks along the edge of the river 65 ft and marks point c. then she walks 25 ft further and marks point d. she turns 90° and walks until her location, point a, and point c are collinear. she marks point e at this location, as shown. (a) can kayla conclude that δ and δ are similar? why or why not? (b) suppose de = 15 ft. what can kayla conclude about the width of the river?

I’m stuck on this equation, anyone got the answer?

Parabolas y=−2x^2 and y=2x^2 +k intersect at points a and b that are in the third and the fourth quadrants respectively. find k if length of the segment ab is 5.