JEE Main 2019 Physics question on Experimental Physics

In a simple pendulum, experiment for determination of acceleration due to gravity $(g)$, time taken for 20 oscillations is measured by using a watch of 1 second least count. The mean value of time taken comes out to be 30 s. The length of pendulum is measured by using a meter scale of least count 1 mm and the value obtained 55.0 cm. The percentage error in the determination of g is close to