Try to get the variable you are looking for by itself by either adding, subtracting, multiplying, or dividing all the things next to it and get it to the other side. once you are done substitute that into the other equations and solve. Then the answer you get you plug it in to the first simplified equation
S = 0.72 m, t=0.63 s s = a · t² /2 0.72 m = a · (0.63 s )² / 2 a · 0.3969 s² = 1.44 m a = 1.44 m : 0.3969 s² = 3.628 m/s² The magnitude of the acceleration due to gravity on the planet is 3.628 m/s²