1st one is not that hard, just draw velocity diagram both water drops have same accelaration which will be 'g', so dv/dt of both graphs should be same, and area of graph shows the distance traveld. Since second drop starts after first one travels 1/4 meters means it started, ((1/4*2)/10)^1/2 will be the time difference.
since those 2 forms triangles the difference of 3/4m comes when area of followinf picture equals 3/4 m. caculation of t is simple geometry.