T=2*\pi*\{sqrt}(l/g)

t/n=2*\pi*\{sqrt}(l/g)

t/(2*/pi*n)=\sqrt{l/g}

t^{2}/(4*\pi^{2}*n^{2}=l/g

g=4*\pi^{2}*n^{2}*l/t^{2}

g=4*3.14^{2}*50^{2}*0.54м/75с^{2}\approx9.46м/с^{2}