I was given the answer, but was confused of how it got to there—please help!

The diameter of a table is 5 feet. what is the circumference

Which ordered pair is a solution to the system of linear equations? 2x + 3y= 6 –3x + 5y = 10

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?