I need help with these question from physics. I decided to take on an extra practice worksheet to study but I'm stuck. Please solve and explain the questions below. Everything is given in the attachments, thanks!!

Question 13 How long must a pendulum be to have a period of 2.3 s on the Moon, where g = 1.6 N/kg? m (Round to the nearest hundredth)Question 15 A mass on a spring oscillates through 20 full cycles in 4s. If the spring constant is 100 N/m, what is the mass? kgQuestion 17 Two friends are resting on an offshore platform after a swim. They estimate that 3.0 m separates a trough and an adjacent crest of each surface wave on the lake. They count 12 crests in 20.0 s. Calculate how fast the waves are moving. (Round to the nearest tenth) m/sQuestion 12 A wave travels through a rope at a speed of 2.1 m/s and has a wavelength of 0.15 m. The wave then passes into a spring where it travels at a speed of 5.0 m/s. The wave's wavelength in the spring is m. (Round to the nearest hundredth)Question 18 A spring has a spring constant of 256 N/m. How far must it be stretched to give it an elastic potential energy of 48 J? (Round to nearest hundredth) m