Half life is 5700 years,that is 50%.
6.25% means 1/16 of the life is left.
T^1/16 =T^1/2*4.
5700 × 4 =22800 years
Answer
given,
mass = 100 kg
acceleration = 10 m/s²
A mass 20 kg slides over 100 kg block
acceleration = 3 m/s²
horizontal friction exerted by the 100 kg block on 20 kg
using newton's second law
F - f = 0
F = f
f = ma
f = 20 × 3
f = 60 N
now net force acting on the 100 kg block
F_net = m a
F_net = 100 x 10
F_net = 1000 N
after 20 kg block falls the acceleration of the bock
F = 1000 +60
F = 1060 N
acceleartion on the block


a = 10.60 m/s²
The answer for your problem is shown on the picture.