I need help with understanding these, if you could put (at least half of) the answers with a slight explanation it would help A LOT

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?

Which of the following contains a variable?

What is the solution to this system of equations? y= 2x - 3.5 x - 2y = -14