Can someone tell me if this is perpendicular? !

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?

A50% increase followed by 33 1/2% decrease

Ade and abc are similar. which best explains why the slope of the line between points a and d is the same as the slope between points a and b?