Both lines AB and CD are secant lines beacuse in two points they are touching the circunference. There is a Theorem which says the following
Since the distance from the center of the circle to each secant line is the same (5 units), we could assume that the both secant lines are similar. saying:
Then the lenght of CD is:
For part 1 you would say the expression is:
I-3 because an expression does not have an equal sign and ingrid swam 3 laps less than holly
For Part 2, you would substitute 25 into l, so it would be 25-3 which equals 22
Hope this helps.