On 7.13, try adding one circle at a time. How many new intersection points do you find each time?

For 7.19 remember the formulas for angles in circles. (For example $\angle BOC = \dfrac{1}{2}\widehat{CB}$.)

On 7.24 proceed similarly to problem 7.2. Remember you can split a regular hexagon into six congruent equilateral triangles.