HELP PLEASE IT'S DUE IN AN HOUR, I also need to understand it for future qs

Answer:
a)5.83cm
Step-by-step explanation:
You have to do 3² × 5² to get the length of AC (the diagonal length of the base of the rectangle) which is √70 or 5.83 rounded to 2 d.p.
not sure about the 2nd bit, but you may have to use trigonometry