Assuming no air resistance, use the formula #v^2 = u^2 - 2as# where #v# is the final velocity, which is #0# since the coin is at rest in its maximum vertical displacement, #u# is the initial velocity, which is #5#, #a# is the acceleration due to gravity and #s# is the displacement of the coin.
So, inputting the values into the formula, you get:
#0^2 = 5^2 - 2*9.81*s#
(The reason I'm using a #- # before #2as# is because the coin is moving upwards, hence it is acting against gravity, so the value of #a# is negative. The original formula is #v^2 = u^2 + 2as#, and since #a# is negative, I've incorporated a #- # to make the calculations simpler.)
#0 = 25 - 19.62s#
#0+19.62s = 25 - 19.62s +19.62s#
#19.62s = 25#
#s = 25/19.62#
#s = 1.27#
#s~~ 1.3m#
