A spring with k = 53 N/m hangs vertically next to the 15 cm mark on the ruler. If a 2.5 kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks

Answer 1

The added load is F = M g = 24.5 N
The spring will stretch by an amount
delta L = F/k = 0.46 m (46 cm)

That will increase the length to the 46 + 15 = 61 cm mark.